From: Sungjong Seo sj1557.seo@samsung.com
commit ff84772fd45d486e4fc78c82e2f70ce5333543e6 upstream.
There is a potential deadlock reported by syzbot as below:
====================================================== WARNING: possible circular locking dependency detected 6.4.0-next-20230707-syzkaller #0 Not tainted ------------------------------------------------------ syz-executor330/5073 is trying to acquire lock: ffff8880218527a0 (&mm->mmap_lock){++++}-{3:3}, at: mmap_read_lock_killable include/linux/mmap_lock.h:151 [inline] ffff8880218527a0 (&mm->mmap_lock){++++}-{3:3}, at: get_mmap_lock_carefully mm/memory.c:5293 [inline] ffff8880218527a0 (&mm->mmap_lock){++++}-{3:3}, at: lock_mm_and_find_vma+0x369/0x510 mm/memory.c:5344 but task is already holding lock: ffff888019f760e0 (&sbi->s_lock){+.+.}-{3:3}, at: exfat_iterate+0x117/0xb50 fs/exfat/dir.c:232
which lock already depends on the new lock.
Chain exists of: &mm->mmap_lock --> mapping.invalidate_lock#3 --> &sbi->s_lock
Possible unsafe locking scenario:
CPU0 CPU1 ---- ---- lock(&sbi->s_lock); lock(mapping.invalidate_lock#3); lock(&sbi->s_lock); rlock(&mm->mmap_lock);
Let's try to avoid above potential deadlock condition by moving dir_emit*() out of sbi->s_lock coverage.
Fixes: ca06197382bd ("exfat: add directory operations") Cc: stable@vger.kernel.org #v5.7+ Reported-by: syzbot+1741a5d9b79989c10bdc@syzkaller.appspotmail.com Link: https://lore.kernel.org/lkml/00000000000078ee7e060066270b@google.com/T/#u Tested-by: syzbot+1741a5d9b79989c10bdc@syzkaller.appspotmail.com Signed-off-by: Sungjong Seo sj1557.seo@samsung.com Signed-off-by: Namjae Jeon linkinjeon@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/exfat/dir.c | 27 ++++++++++++--------------- 1 file changed, 12 insertions(+), 15 deletions(-)
--- a/fs/exfat/dir.c +++ b/fs/exfat/dir.c @@ -211,7 +211,10 @@ static void exfat_free_namebuf(struct ex exfat_init_namebuf(nb); }
-/* skip iterating emit_dots when dir is empty */ +/* + * Before calling dir_emit*(), sbi->s_lock should be released + * because page fault can occur in dir_emit*(). + */ #define ITER_POS_FILLED_DOTS (2) static int exfat_iterate(struct file *filp, struct dir_context *ctx) { @@ -226,11 +229,10 @@ static int exfat_iterate(struct file *fi int err = 0, fake_offset = 0;
exfat_init_namebuf(nb); - mutex_lock(&EXFAT_SB(sb)->s_lock);
cpos = ctx->pos; if (!dir_emit_dots(filp, ctx)) - goto unlock; + goto out;
if (ctx->pos == ITER_POS_FILLED_DOTS) { cpos = 0; @@ -242,16 +244,18 @@ static int exfat_iterate(struct file *fi /* name buffer should be allocated before use */ err = exfat_alloc_namebuf(nb); if (err) - goto unlock; + goto out; get_new: + mutex_lock(&EXFAT_SB(sb)->s_lock); + if (ei->flags == ALLOC_NO_FAT_CHAIN && cpos >= i_size_read(inode)) goto end_of_dir;
err = exfat_readdir(inode, &cpos, &de); if (err) { /* - * At least we tried to read a sector. Move cpos to next sector - * position (should be aligned). + * At least we tried to read a sector. + * Move cpos to next sector position (should be aligned). */ if (err == -EIO) { cpos += 1 << (sb->s_blocksize_bits); @@ -274,16 +278,10 @@ get_new: inum = iunique(sb, EXFAT_ROOT_INO); }
- /* - * Before calling dir_emit(), sb_lock should be released. - * Because page fault can occur in dir_emit() when the size - * of buffer given from user is larger than one page size. - */ mutex_unlock(&EXFAT_SB(sb)->s_lock); if (!dir_emit(ctx, nb->lfn, strlen(nb->lfn), inum, (de.attr & ATTR_SUBDIR) ? DT_DIR : DT_REG)) - goto out_unlocked; - mutex_lock(&EXFAT_SB(sb)->s_lock); + goto out; ctx->pos = cpos; goto get_new;
@@ -291,9 +289,8 @@ end_of_dir: if (!cpos && fake_offset) cpos = ITER_POS_FILLED_DOTS; ctx->pos = cpos; -unlock: mutex_unlock(&EXFAT_SB(sb)->s_lock); -out_unlocked: +out: /* * To improve performance, free namebuf after unlock sb_lock. * If namebuf is not allocated, this function do nothing