Memory use after free in the WIP TA library

o/

Running some quick fuzzing, I noticed there is a use after free (in the master branch) using clang's static analyzer "scan-build". File is ta/ta.c at line 78.

mpv version and platform versions

Git master - git show commit 6c1f01d2841281fd594f8ce874b4113640c07553 (HEAD -> master, origin/master, origin/HEAD)

Reproduction steps

After installing build dependencies and scan-build otherwise I don't think meson generates a ninja target for it, (I'm on Ubuntu 22.04.1),

meson build -Db_sanitize=address
ninja -C build scan-build

The -Db_sanitize=address enables libasan, not necessary for this.

The scan-build target is made by meson, so I just invoke it. It reconfigures the meson project, builds it and uses clang's static analyzer.

The output I really am noticing here, because I don't feel like digging into the player for the other things is:

[209/244] Compiling C object mpv.p/ta_ta.c.o
../../../ta/ta.c:78:5: warning: Use of memory after it is freed [unix.Malloc]
    return h;
    ^~~~~~~~
../../../ta/ta.c:353:39: warning: Access to field 'leak_prev' results in a dereference of a null pointer (loaded from field 'leak_next') [core.NullDereference]
            cur->leak_next->leak_prev = cur->leak_prev;
                 ~~~~~~~~~            ^
2 warnings generated.

Expected behavior

I guess, for there to not be anything /shrug

Actual behavior

[209/244] Compiling C object mpv.p/ta_ta.c.o
../../../ta/ta.c:78:5: warning: Use of memory after it is freed [unix.Malloc]
    return h;
    ^~~~~~~~
../../../ta/ta.c:353:39: warning: Access to field 'leak_prev' results in a dereference of a null pointer (loaded from field 'leak_next') [core.NullDereference]
            cur->leak_next->leak_prev = cur->leak_prev;
                 ~~~~~~~~~            ^
2 warnings generated.

The ta_header struct calls return(h); - if ta_free() was called and the code jumps to the header, it is a UAF

Log file

So scan-build conveniently puts everything in a log, even into a set of HTML pages that can be viewed using scan-view.
2022-08-22-220138-87585-1.zip

other stuff

Was originally going to report with huntr for a CVE, but the README says you guys don't use ta in anything so I thought this would be more of a bug report

Start with ta/ta.c at lines 78 and 353, then reproduce the analyzer output using meson build -Db_sanitize=address followed by ninja -C build scan-build. Trace the reported use-after-free and null dereference in the ta_header and leak-list paths; done means the scan-build warnings no longer appear without introducing new failures.