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author | Axel Rasmussen <axelrasmussen@google.com> | 2021-05-15 03:27:19 +0300 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-05-19 11:13:11 +0300 |
commit | 140cfd9980124aecb6c03ef2e69c72d0548744de (patch) | |
tree | fe0e35476296b3599ec09ac85a94e08eb9785883 /mm/shmem.c | |
parent | 2ed1d90162a0c0683ecbe0c4802187fa22d641c3 (diff) | |
download | linux-140cfd9980124aecb6c03ef2e69c72d0548744de.tar.xz |
userfaultfd: release page in error path to avoid BUG_ON
commit 7ed9d238c7dbb1fdb63ad96a6184985151b0171c upstream.
Consider the following sequence of events:
1. Userspace issues a UFFD ioctl, which ends up calling into
shmem_mfill_atomic_pte(). We successfully account the blocks, we
shmem_alloc_page(), but then the copy_from_user() fails. We return
-ENOENT. We don't release the page we allocated.
2. Our caller detects this error code, tries the copy_from_user() after
dropping the mmap_lock, and retries, calling back into
shmem_mfill_atomic_pte().
3. Meanwhile, let's say another process filled up the tmpfs being used.
4. So shmem_mfill_atomic_pte() fails to account blocks this time, and
immediately returns - without releasing the page.
This triggers a BUG_ON in our caller, which asserts that the page
should always be consumed, unless -ENOENT is returned.
To fix this, detect if we have such a "dangling" page when accounting
fails, and if so, release it before returning.
Link: https://lkml.kernel.org/r/20210428230858.348400-1-axelrasmussen@google.com
Fixes: cb658a453b93 ("userfaultfd: shmem: avoid leaking blocks and used blocks in UFFDIO_COPY")
Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
Reported-by: Hugh Dickins <hughd@google.com>
Acked-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'mm/shmem.c')
-rw-r--r-- | mm/shmem.c | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/mm/shmem.c b/mm/shmem.c index 537c137698f8..ffc8b4ccbea6 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -2378,8 +2378,18 @@ static int shmem_mfill_atomic_pte(struct mm_struct *dst_mm, pgoff_t offset, max_off; ret = -ENOMEM; - if (!shmem_inode_acct_block(inode, 1)) + if (!shmem_inode_acct_block(inode, 1)) { + /* + * We may have got a page, returned -ENOENT triggering a retry, + * and now we find ourselves with -ENOMEM. Release the page, to + * avoid a BUG_ON in our caller. + */ + if (unlikely(*pagep)) { + put_page(*pagep); + *pagep = NULL; + } goto out; + } if (!*pagep) { page = shmem_alloc_page(gfp, info, pgoff); |