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fat: work around race with userspace's read via blockdev while mounting
[ Upstream commit 07bfa4415a
]
If userspace reads the buffer via blockdev while mounting,
sb_getblk()+modify can race with buffer read via blockdev.
For example,
FS userspace
bh = sb_getblk()
modify bh->b_data
read
ll_rw_block(bh)
fill bh->b_data by on-disk data
/* lost modified data by FS */
set_buffer_uptodate(bh)
set_buffer_uptodate(bh)
Userspace should not use the blockdev while mounting though, the udev
seems to be already doing this. Although I think the udev should try to
avoid this, workaround the race by small overhead.
Link: http://lkml.kernel.org/r/87pnk7l3sw.fsf_-_@mail.parknet.co.jp
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Reported-by: Jan Stancek <jstancek@redhat.com>
Tested-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
parent
735ad03318
commit
3554b8a172
13
fs/fat/dir.c
13
fs/fat/dir.c
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@ -1097,8 +1097,11 @@ static int fat_zeroed_cluster(struct inode *dir, sector_t blknr, int nr_used,
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err = -ENOMEM;
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goto error;
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}
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/* Avoid race with userspace read via bdev */
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lock_buffer(bhs[n]);
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memset(bhs[n]->b_data, 0, sb->s_blocksize);
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set_buffer_uptodate(bhs[n]);
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unlock_buffer(bhs[n]);
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mark_buffer_dirty_inode(bhs[n], dir);
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n++;
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@ -1155,6 +1158,8 @@ int fat_alloc_new_dir(struct inode *dir, struct timespec *ts)
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fat_time_unix2fat(sbi, ts, &time, &date, &time_cs);
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de = (struct msdos_dir_entry *)bhs[0]->b_data;
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/* Avoid race with userspace read via bdev */
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lock_buffer(bhs[0]);
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/* filling the new directory slots ("." and ".." entries) */
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memcpy(de[0].name, MSDOS_DOT, MSDOS_NAME);
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memcpy(de[1].name, MSDOS_DOTDOT, MSDOS_NAME);
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@ -1177,6 +1182,7 @@ int fat_alloc_new_dir(struct inode *dir, struct timespec *ts)
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de[0].size = de[1].size = 0;
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memset(de + 2, 0, sb->s_blocksize - 2 * sizeof(*de));
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set_buffer_uptodate(bhs[0]);
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unlock_buffer(bhs[0]);
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mark_buffer_dirty_inode(bhs[0], dir);
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err = fat_zeroed_cluster(dir, blknr, 1, bhs, MAX_BUF_PER_PAGE);
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@ -1234,11 +1240,14 @@ static int fat_add_new_entries(struct inode *dir, void *slots, int nr_slots,
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/* fill the directory entry */
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copy = min(size, sb->s_blocksize);
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/* Avoid race with userspace read via bdev */
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lock_buffer(bhs[n]);
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memcpy(bhs[n]->b_data, slots, copy);
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set_buffer_uptodate(bhs[n]);
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unlock_buffer(bhs[n]);
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mark_buffer_dirty_inode(bhs[n], dir);
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slots += copy;
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size -= copy;
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set_buffer_uptodate(bhs[n]);
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mark_buffer_dirty_inode(bhs[n], dir);
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if (!size)
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break;
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n++;
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@ -389,8 +389,11 @@ static int fat_mirror_bhs(struct super_block *sb, struct buffer_head **bhs,
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err = -ENOMEM;
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goto error;
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}
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/* Avoid race with userspace read via bdev */
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lock_buffer(c_bh);
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memcpy(c_bh->b_data, bhs[n]->b_data, sb->s_blocksize);
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set_buffer_uptodate(c_bh);
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unlock_buffer(c_bh);
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mark_buffer_dirty_inode(c_bh, sbi->fat_inode);
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if (sb->s_flags & MS_SYNCHRONOUS)
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err = sync_dirty_buffer(c_bh);
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