diff options
| author | Matheus Alves de Almeida <matheus.aalmeida@inf.ufrgs.br> | 2026-10-21 13:21:04 -0300 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2026-11-02 19:18:56 -0800 |
| commit | 7b90009546f5d3f3ac9428040cd7ffbdfd60f2eb (patch) | |
| tree | a1f042960deb04124ceca1273c15e197564406e1 | |
| parent | 4bdfe8dd2342f9c2bdc3b788699164ebe21d9126 (diff) | |
fat: hold truncate_lock in fat_write_failed()
The current fat_write_failed() implementation calls into
fat_truncate_blocks() without holding truncate_lock.
A failed or short extending write racing with FIBMAP can spuriously make a
FAT filesystem read-only. FIBMAP bounds its lookup by i_blocks, so it can
walk allocated clusters beyond i_size while fat_write_failed() is removing
them. If the chain is shortened during the walk, the mapper can report a
bogus "request beyond EOF" error, triggering the default read-only error
policy. Hold truncate_lock for write around the block cleanup to
serialize it with _fat_bmap().
For comparison, fat_setattr() correctly holds truncate_lock during
truncation:
down_write(&MSDOS_I(inode)->truncate_lock);
truncate_setsize(inode, attr->ia_size);
fat_truncate_blocks(inode, attr->ia_size);
up_write(&MSDOS_I(inode)->truncate_lock);
Make it so ->truncate_lock is held exclusive while truncating.
Link: https://lore.kernel.org/20261021162105.62525-1-matheus.aalmeida@inf.ufrgs.br
Fixes: 16fab2015099 ("fat: permit to return phy block number by fibmap in fallocated region")
Fixes: 459f6ed3b8c7 ("fat: convert to use the new truncate convention.")
Signed-off-by: Matheus Alves de Almeida <matheus.aalmeida@inf.ufrgs.br>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Pedro Falcato <pfalcato@suse.de>
Cc: <stable@vger.kernel.org>
| -rw-r--r-- | fs/fat/inode.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/fs/fat/inode.c b/fs/fat/inode.c index d85c8fbdcca4..353c91f0a843 100644 --- a/fs/fat/inode.c +++ b/fs/fat/inode.c @@ -217,7 +217,9 @@ static void fat_write_failed(struct address_space *mapping, loff_t to) if (to > inode->i_size) { truncate_pagecache(inode, inode->i_size); + down_write(&MSDOS_I(inode)->truncate_lock); fat_truncate_blocks(inode, inode->i_size); + up_write(&MSDOS_I(inode)->truncate_lock); } } |