Date: Thu, 24 Apr 2025 13:21:18 GMT From: Mark Johnston <markj@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org Subject: git: 1065a7ebdeb8 - stable/14 - posixshm: Fix range locking in shm_write() Message-ID: <202504241321.53ODLI1Z038228@gitrepo.freebsd.org>
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The branch stable/14 has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=1065a7ebdeb8fb16ab6a5112cc4845b66c467eb9 commit 1065a7ebdeb8fb16ab6a5112cc4845b66c467eb9 Author: Mark Johnston <markj@FreeBSD.org> AuthorDate: 2025-04-06 22:51:53 +0000 Commit: Mark Johnston <markj@FreeBSD.org> CommitDate: 2025-04-24 13:20:52 +0000 posixshm: Fix range locking in shm_write() There is a somewhat strange case where when writing to a POSIX shm object, the object is not allowed to grow, and the I/O offset+length overflows. In that case we simply truncate the I/O to the object size. Later we write-lock the range [offset, objsize). However, we were not checking whether offset > objsize, in which case we're writing zero bytes but locking an invalid range. Modify the range locking in shm_write() to take this possibility into account. While here, rename a variable to make its purpose a bit more clear, and add an assertion against negative offsets (which is supposed to be enforced by the caller of fo_write for I/O to files that aren't character devices). Reported by: syzkaller Reviewed by: kevans, kib MFC after: 2 weeks Differential Revision: https://reviews.freebsd.org/D49673 (cherry picked from commit 82d8c609cfb7c6d8a9da8e30efa54240f293359e) --- sys/kern/uipc_shm.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) diff --git a/sys/kern/uipc_shm.c b/sys/kern/uipc_shm.c index e159c802795b..c8d5521c5ab1 100644 --- a/sys/kern/uipc_shm.c +++ b/sys/kern/uipc_shm.c @@ -481,7 +481,10 @@ shm_write(struct file *fp, struct uio *uio, struct ucred *active_cred, struct shmfd *shmfd; void *rl_cookie; int error; - off_t size; + off_t newsize; + + KASSERT((flags & FOF_OFFSET) == 0 || uio->uio_offset >= 0, + ("%s: negative offset", __func__)); shmfd = fp->f_data; #ifdef MAC @@ -503,21 +506,23 @@ shm_write(struct file *fp, struct uio *uio, struct ucred *active_cred, return (EFBIG); } - size = shmfd->shm_size; + newsize = atomic_load_64(&shmfd->shm_size); } else { - size = uio->uio_offset + uio->uio_resid; + newsize = uio->uio_offset + uio->uio_resid; } if ((flags & FOF_OFFSET) == 0) rl_cookie = shm_rangelock_wlock(shmfd, 0, OFF_MAX); else - rl_cookie = shm_rangelock_wlock(shmfd, uio->uio_offset, size); + rl_cookie = shm_rangelock_wlock(shmfd, uio->uio_offset, + MAX(newsize, uio->uio_offset)); if ((shmfd->shm_seals & F_SEAL_WRITE) != 0) { error = EPERM; } else { error = 0; if ((shmfd->shm_flags & SHM_GROW_ON_WRITE) != 0 && - size > shmfd->shm_size) { - error = shm_dotruncate_cookie(shmfd, size, rl_cookie); + newsize > shmfd->shm_size) { + error = shm_dotruncate_cookie(shmfd, newsize, + rl_cookie); } if (error == 0) error = uiomove_object(shmfd->shm_object,
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