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author | Rich Felker <dalias@aerifal.cx> | 2018-04-17 23:59:41 -0400 |
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committer | Rich Felker <dalias@aerifal.cx> | 2018-04-18 14:22:49 -0400 |
commit | c21f750727515602a9e84f2a190ee8a0a2aeb2a1 (patch) | |
tree | e15b0c717d481c2d7e9fa0a7baeb380f91fe9d0e /src/stdio/flockfile.c | |
parent | 502027540bafd0681bfc46b0ae28639e51bba6a6 (diff) | |
download | musl-c21f750727515602a9e84f2a190ee8a0a2aeb2a1.tar.gz musl-c21f750727515602a9e84f2a190ee8a0a2aeb2a1.tar.xz musl-c21f750727515602a9e84f2a190ee8a0a2aeb2a1.zip |
fix stdio lock dependency on read-after-free not faulting
instead of using a waiters count, add a bit to the lock field indicating that the lock may have waiters. threads which obtain the lock after contending for it will perform a potentially-spurious wake when they release the lock.
Diffstat (limited to 'src/stdio/flockfile.c')
-rw-r--r-- | src/stdio/flockfile.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/src/stdio/flockfile.c b/src/stdio/flockfile.c index a196c1ef..6b574cf0 100644 --- a/src/stdio/flockfile.c +++ b/src/stdio/flockfile.c @@ -1,10 +1,14 @@ #include "stdio_impl.h" #include "pthread_impl.h" +#define MAYBE_WAITERS 0x40000000 + void flockfile(FILE *f) { while (ftrylockfile(f)) { int owner = f->lock; - if (owner) __wait(&f->lock, &f->waiters, owner, 1); + if (!owner) continue; + a_cas(&f->lock, owner, owner|MAYBE_WAITERS); + __futexwait(&f->lock, owner|MAYBE_WAITERS, 1); } } |