bug(cp): --attributes-only, there was no self file check it can lead to race conditions

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#13,161 opened on Jun 28, 2026 1 comment 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty: 3/5
Estimated time: 1-2 days
Newbie friendliness: 48/100

Issue type: Bug
Clarity: Mostly clear
Activity status: Quiet
Tech stack: rust
Domain: cli

Research direction

Start in src/uu/cp and trace the handling of --attributes-only for identical source and destination paths. Reproduce the reported ./cp --attributes-only a a case, then inspect the existing self-copy checks and add coverage for this path. Done means identical files are detected safely without the operation creating a race condition.

Written by the indexing model from the issue text.

Description

U - cp

Hi, uutils mainteners

we confirmed that the --attributes-only cp option do not have a check at all for the same files, as we confirmed

relunsec@relunsec:~/software/coreutils/target/debug$ strace ./cp --attributes-only a a
execve("./cp", ["./cp", "--attributes-only", "a", "a"], 0x7ffe45bae8f8 /* 74 vars */) = 0
brk(NULL)                               = 0x5d5c03c66000
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x78cd43a98000
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
openat(AT_FDCWD, "/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=97781, ...}) = 0
mmap(NULL, 97781, PROT_READ, MAP_PRIVATE, 3, 0) = 0x78cd43a80000
close(3)                                = 0
openat(AT_FDCWD, "/usr/lib/x86_64-linux-gnu/libgcc_s.so.1", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\0\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0644, st_size=187120, ...}) = 0
mmap(NULL, 185256, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x78cd43a52000
mmap(0x78cd43a56000, 147456, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x4000) = 0x78cd43a56000
mmap(0x78cd43a7a000, 16384, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x28000) = 0x78cd43a7a000
mmap(0x78cd43a7e000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2c000) = 0x78cd43a7e000
close(3)                                = 0
openat(AT_FDCWD, "/usr/lib/x86_64-linux-gnu/libm.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\0\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0644, st_size=1198376, ...}) = 0
mmap(NULL, 1200152, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x78cd4392c000
mmap(0x78cd4393e000, 655360, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x12000) = 0x78cd4393e000
mmap(0x78cd439de000, 466944, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0xb2000) = 0x78cd439de000
mmap(0x78cd43a50000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x123000) = 0x78cd43a50000
close(3)                                = 0
openat(AT_FDCWD, "/usr/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0 \250\2\0\0\0\0\0"..., 832) = 832
pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 840, 64) = 840
fstat(3, {st_mode=S_IFREG|0755, st_size=2186512, ...}) = 0
pread64(3, "\6\0\0\0\4\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0@\0\0\0\0\0\0\0"..., 840, 64) = 840
mmap(NULL, 2231696, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x78cd4370b000
mmap(0x78cd43733000, 1671168, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x28000) = 0x78cd43733000
mmap(0x78cd438cb000, 319488, PROT_READ, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1c0000) = 0x78cd438cb000
mmap(0x78cd43919000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x20d000) = 0x78cd43919000
mmap(0x78cd4391f000, 52624, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x78cd4391f000
close(3)                                = 0
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x78cd43709000
arch_prctl(ARCH_SET_FS, 0x78cd43709d80) = 0
set_tid_address(0x78cd4370a3a8)         = 87544
set_robust_list(0x78cd4370a060, 24)     = 0
rseq(0x78cd43709ac0, 0x21, 0, 0x53053053) = 0
mprotect(0x78cd43919000, 16384, PROT_READ) = 0
mprotect(0x78cd43a50000, 4096, PROT_READ) = 0
mprotect(0x78cd43a7e000, 4096, PROT_READ) = 0
mprotect(0x5d5bfa7c3000, 196608, PROT_READ) = 0
mprotect(0x78cd43add000, 8192, PROT_READ) = 0
prlimit64(0, RLIMIT_STACK, NULL, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0
getrandom("\xe6\x83\xce\xd5\xb1\x64\x61\x45", 8, GRND_NONBLOCK) = 8
munmap(0x78cd43a80000, 97781)           = 0
fcntl(0, F_GETFD)                       = 0
fcntl(1, F_GETFD)                       = 0
fcntl(2, F_GETFD)                       = 0
rt_sigaction(SIGPIPE, NULL, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=0}, 8) = 0
poll([{fd=0, events=0}, {fd=1, events=0}, {fd=2, events=0}], 3, 0) = 0 (Timeout)
rt_sigaction(SIGPIPE, {sa_handler=SIG_IGN, sa_mask=[PIPE], sa_flags=SA_RESTORER|SA_RESTART, sa_restorer=0x78cd43750cb0}, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=0}, 8) = 0
brk(NULL)                               = 0x5d5c03c66000
brk(0x5d5c03c87000)                     = 0x5d5c03c87000
openat(AT_FDCWD, "/proc/self/maps", O_RDONLY|O_CLOEXEC) = 3
prlimit64(0, RLIMIT_STACK, NULL, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0
fstat(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0
read(3, "5d5bfa372000-5d5bfa511000 r--p 0"..., 1024) = 1024
read(3, "r/lib/x86_64-linux-gnu/libc.so.6"..., 1024) = 1024
read(3, "           /usr/lib/x86_64-linux"..., 1024) = 1024
read(3, "nux-gnu/ld-linux-x86-64.so.2\n78c"..., 1024) = 363
lseek(3, 0, SEEK_CUR)                   = 3435
lseek(3, 3351, SEEK_SET)                = 3351
close(3)                                = 0
sched_getaffinity(87544, 32, [0 1 2 3 4 5 6 7]) = 8
rt_sigaction(SIGSEGV, NULL, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=0}, 8) = 0
sigaltstack(NULL, {ss_sp=NULL, ss_flags=SS_DISABLE, ss_size=0}) = 0
mmap(NULL, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_STACK, -1, 0) = 0x78cd43a95000
mprotect(0x78cd43a95000, 4096, PROT_NONE) = 0
sigaltstack({ss_sp=0x78cd43a96000, ss_flags=0, ss_size=8192}, NULL) = 0
gettid()                                = 87544
rt_sigaction(SIGSEGV, {sa_handler=0x5d5bfa7a1710, sa_mask=[], sa_flags=SA_RESTORER|SA_ONSTACK|SA_SIGINFO, sa_restorer=0x78cd43750cb0}, NULL, 8) = 0
rt_sigaction(SIGBUS, NULL, {sa_handler=SIG_DFL, sa_mask=[], sa_flags=0}, 8) = 0
rt_sigaction(SIGBUS, {sa_handler=0x5d5bfa7a1710, sa_mask=[], sa_flags=SA_RESTORER|SA_ONSTACK|SA_SIGINFO, sa_restorer=0x78cd43750cb0}, NULL, 8) = 0
statx(AT_FDCWD, "/home/relunsec/software/coreutils/src/uucore/../uu/cp/locales", AT_STATX_SYNC_AS_STAT, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFDIR|0775, stx_size=4, ...}) = 0
readlink("/home", 0x7fff37a2d570, 1023) = -1 EINVAL (Invalid argument)
readlink("/home/relunsec", 0x7fff37a2d570, 1023) = -1 EINVAL (Invalid argument)
readlink("/home/relunsec/software", 0x7fff37a2d570, 1023) = -1 EINVAL (Invalid argument)
readlink("/home/relunsec/software/coreutils", 0x7fff37a2d570, 1023) = -1 EINVAL (Invalid argument)
readlink("/home/relunsec/software/coreutils/src", 0x7fff37a2d570, 1023) = -1 EINVAL (Invalid argument)
readlink("/home/relunsec/software/coreutils/src/uucore", 0x7fff37a2d570, 1023) = -1 EINVAL (Invalid argument)
faccessat2(AT_FDCWD, "/home/relunsec/software/coreutils/src/uucore/", F_OK, AT_EACCESS) = 0
readlink("/home/relunsec/software/coreutils/src/uu", 0x7fff37a2d570, 1023) = -1 EINVAL (Invalid argument)
readlink("/home/relunsec/software/coreutils/src/uu/cp", 0x7fff37a2d570, 1023) = -1 EINVAL (Invalid argument)
readlink("/home/relunsec/software/coreutils/src/uu/cp/locales", 0x7fff37a2d570, 1023) = -1 EINVAL (Invalid argument)
statx(AT_FDCWD, "/home/relunsec/software/coreutils/src/uucore/locales", AT_STATX_SYNC_AS_STAT, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFDIR|0775, stx_size=4, ...}) = 0
openat(AT_FDCWD, "/home/relunsec/software/coreutils/src/uucore/locales/en-US.ftl", O_RDONLY|O_CLOEXEC) = 3
statx(3, "", AT_STATX_SYNC_AS_STAT|AT_EMPTY_PATH, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0664, stx_size=4113, ...}) = 0
read(3, "# Common strings shared across a"..., 4113) = 4113
read(3, "", 32)                         = 0
close(3)                                = 0
statx(AT_FDCWD, "/home/relunsec/software/coreutils/src/uucore/../uu/cp/locales", AT_STATX_SYNC_AS_STAT, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFDIR|0775, stx_size=4, ...}) = 0
openat(AT_FDCWD, "/home/relunsec/software/coreutils/src/uucore/../uu/cp/locales/en-US.ftl", O_RDONLY|O_CLOEXEC) = 3
statx(3, "", AT_STATX_SYNC_AS_STAT|AT_EMPTY_PATH, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0664, stx_size=8247, ...}) = 0
read(3, "cp-about = Copy SOURCE to DEST, "..., 8247) = 8247
read(3, "", 32)                         = 0
close(3)                                = 0
brk(0x5d5c03ca9000)                     = 0x5d5c03ca9000
rt_sigaction(SIGPIPE, {sa_handler=SIG_DFL, sa_mask=[PIPE], sa_flags=SA_RESTORER|SA_RESTART, sa_restorer=0x78cd43750cb0}, {sa_handler=SIG_IGN, sa_mask=[PIPE], sa_flags=SA_RESTORER|SA_RESTART, sa_restorer=0x78cd43750cb0}, 8) = 0
rt_sigaction(SIGSEGV, {sa_handler=SIG_DFL, sa_mask=~[RTMIN RT_1], sa_flags=SA_RESTORER, sa_restorer=0x78cd43750cb0}, {sa_handler=0x5d5bfa7a1710, sa_mask=[], sa_flags=SA_RESTORER|SA_ONSTACK|SA_SIGINFO, sa_restorer=0x78cd43750cb0}, 8) = 0
rt_sigaction(SIGBUS, {sa_handler=SIG_DFL, sa_mask=~[RTMIN RT_1], sa_flags=SA_RESTORER, sa_restorer=0x78cd43750cb0}, {sa_handler=0x5d5bfa7a1710, sa_mask=[], sa_flags=SA_RESTORER|SA_ONSTACK|SA_SIGINFO, sa_restorer=0x78cd43750cb0}, 8) = 0
ioctl(1, TCGETS2, {c_iflag=BRKINT|IGNPAR|ICRNL|IXON|IMAXBEL, c_oflag=NL0|CR0|TAB0|BS0|VT0|FF0|OPOST|ONLCR, c_cflag=B38400|CS8|CREAD, c_lflag=ISIG|ICANON|ECHO|ECHOE|ECHOK|IEXTEN|ECHOCTL|ECHOKE, ...}) = 0
statx(AT_FDCWD, "a", AT_STATX_SYNC_AS_STAT, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0664, stx_size=6, ...}) = 0
statx(AT_FDCWD, "a", AT_STATX_SYNC_AS_STAT, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0664, stx_size=6, ...}) = 0
rt_sigprocmask(SIG_BLOCK, ~[], [], 8)   = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_DROPPABLE|MAP_ANONYMOUS, -1, 0) = 0x78cd43a94000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x78cd43a93000
rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0
getrandom("\x3c\x1b\xba\x04\x85\x19\x4c\x05\xc1\xce\xf8\x85\x40\x2c\xfc\x72\x82\x99\x1a\xc1\xb0\x3a\x4f\x45\x50\xa3\x43\x53\xc5\x7e\x04\x45", 32, 0) = 32
newfstatat(AT_FDCWD, "a", {st_mode=S_IFREG|0664, st_size=6, ...}, 0) = 0
statx(AT_FDCWD, "a", AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0664, stx_size=6, ...}) = 0
statx(AT_FDCWD, "a", AT_STATX_SYNC_AS_STAT, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0664, stx_size=6, ...}) = 0
statx(AT_FDCWD, "a", AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0664, stx_size=6, ...}) = 0
statx(AT_FDCWD, "a", AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0664, stx_size=6, ...}) = 0
statx(AT_FDCWD, "a", AT_STATX_SYNC_AS_STAT, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0664, stx_size=6, ...}) = 0
statx(AT_FDCWD, "a", AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0664, stx_size=6, ...}) = 0
statx(AT_FDCWD, "a", AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0664, stx_size=6, ...}) = 0
statx(AT_FDCWD, "a", AT_STATX_SYNC_AS_STAT, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0664, stx_size=6, ...}) = 0
statx(AT_FDCWD, "a", AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0664, stx_size=6, ...}) = 0
openat(AT_FDCWD, "a", O_WRONLY|O_CREAT|O_CLOEXEC, 0666) = 3
fcntl(3, F_GETFD)                       = 0x1 (flags FD_CLOEXEC)
close(3)                                = 0
chmod("a", 0100664)                     = 0
getcwd("/home/relunsec/software/coreutils/target/debug", 512) = 47
readlink("/home", 0x7fff37a2ae10, 1023) = -1 EINVAL (Invalid argument)
readlink("/home/relunsec", 0x7fff37a2ae10, 1023) = -1 EINVAL (Invalid argument)
readlink("/home/relunsec/software", 0x7fff37a2ae10, 1023) = -1 EINVAL (Invalid argument)
readlink("/home/relunsec/software/coreutils", 0x7fff37a2ae10, 1023) = -1 EINVAL (Invalid argument)
readlink("/home/relunsec/software/coreutils/target", 0x7fff37a2ae10, 1023) = -1 EINVAL (Invalid argument)
readlink("/home/relunsec/software/coreutils/target/debug", 0x7fff37a2ae10, 1023) = -1 EINVAL (Invalid argument)
statx(AT_FDCWD, "/", AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=STATX_ATTR_MOUNT_ROOT, stx_mode=S_IFDIR|0755, stx_size=29, ...}) = 0
statx(AT_FDCWD, "/home", AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=STATX_ATTR_MOUNT_ROOT, stx_mode=S_IFDIR|0755, stx_size=8, ...}) = 0
statx(AT_FDCWD, "/home/relunsec", AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFDIR|0755, stx_size=275, ...}) = 0
statx(AT_FDCWD, "/home/relunsec/software", AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFDIR|0775, stx_size=39, ...}) = 0
statx(AT_FDCWD, "/home/relunsec/software/coreutils", AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFDIR|0775, stx_size=42, ...}) = 0
statx(AT_FDCWD, "/home/relunsec/software/coreutils/target", AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFDIR|0775, stx_size=5, ...}) = 0
statx(AT_FDCWD, "/home/relunsec/software/coreutils/target/debug", AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFDIR|0775, stx_size=448, ...}) = 0
statx(AT_FDCWD, "/home/relunsec/software/coreutils/target/debug/a", AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0664, stx_size=6, ...}) = 0
statx(AT_FDCWD, "/home/relunsec/software/coreutils/target/debug/a", AT_STATX_SYNC_AS_STAT, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0664, stx_size=6, ...}) = 0
statx(AT_FDCWD, "/home/relunsec/software/coreutils/target/debug/a", AT_STATX_SYNC_AS_STAT, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0664, stx_size=6, ...}) = 0
statx(AT_FDCWD, "/home/relunsec/software/coreutils/target/debug/a", AT_STATX_SYNC_AS_STAT|AT_SYMLINK_NOFOLLOW, STATX_ALL, {stx_mask=STATX_ALL|STATX_MNT_ID, stx_attributes=0, stx_mode=S_IFREG|0664, stx_size=6, ...}) = 0
newfstatat(AT_FDCWD, "a", {st_mode=S_IFREG|0664, st_size=6, ...}, 0) = 0
sigaltstack({ss_sp=NULL, ss_flags=SS_DISABLE, ss_size=8192}, NULL) = 0
munmap(0x78cd43a95000, 12288)           = 0
exit_group(0)                           = ?
+++ exited with 0 +++
relunsec@relunsec:~/software/coreutils/target/debug$ 
relunsec@relunsec:~/software/coreutils/target/debug$ gnucp --attributes-only a a
gnucp: 'a' and 'a' are the same file
relunsec@relunsec:~/software/coreutils/target/debug$ gnucp --attributes-only a ./a
gnucp: 'a' and './a' are the same file
relunsec@relunsec:~/software/coreutils/target/debug$

while the gnu one have

and very critically, look

openat(AT_FDCWD, "a", O_WRONLY|O_CREAT|O_CLOEXEC, 0666) = 3
chmod("a", 0100664) = 0

chmod called against a file path not the fd 3, it can lead to race conditions

Dominant language: Rust
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