From 31e5e0c8c8e2617eb9f7a20c1cf5df23f592ade2 Mon Sep 17 00:00:00 2001 From: Deepanshu Kartikey Date: Sun, 21 Jun 2026 09:28:41 +0530 Subject: [PATCH] udf: avoid recursive s_alloc_mutex deadlock when freeing AED blocks udf_table_prealloc_blocks() and udf_table_new_block() call udf_delete_aext() on the unallocated-space-table inode while holding sbi->s_alloc_mutex. When the deleted allocation descriptor empties an allocation-extent (AED) block, udf_delete_aext() returns that block to free space via udf_free_blocks(). For a table-managed partition that path is udf_free_blocks() -> udf_table_free_blocks() -> mutex_lock(&sbi->s_alloc_mutex), i.e. the task tries to acquire a mutex it already holds. On a PREEMPT_RT kernel the rtmutex deadlock detector reports this as -EDEADLK: rtmutex deadlock detected WARNING: kernel/locking/rtmutex.c:1698 at rt_mutex_handle_deadlock udf_table_free_blocks fs/udf/balloc.c:376 [inline] udf_free_blocks+0xa8c/0x1900 fs/udf/balloc.c:678 udf_delete_aext+0x4f5/0xc00 fs/udf/inode.c:2381 udf_table_prealloc_blocks fs/udf/balloc.c:544 [inline] udf_prealloc_blocks+0xbd4/0x10e0 fs/udf/balloc.c:702 On a non-RT kernel the same path is a hard self-deadlock (or a lockdep recursive-locking splat). It is reachable from a crafted UDF image via the write/sendfile path. The allocator already refuses to recurse on the add side: see the comment in udf_table_free_blocks() explaining why it must not call udf_add_aext() while holding s_alloc_mutex. Apply the same rule to the delete side. Let udf_delete_aext() report the AED block it would otherwise free through a new out-parameter, and have the two callers that hold s_alloc_mutex free it after dropping the lock. The block is already unlinked from the inode's descriptor chain by then, so nothing can reference it in the meantime. All other callers pass NULL and keep freeing the block inline, exactly as before. The out-parameter is pre-initialised with the reserved partition number 0xFFFF, which can never name a real block, so the caller can tell whether a block was handed back. Reported-by: syzbot+6a680377e13041c19d50@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=6a680377e13041c19d50 Signed-off-by: Deepanshu Kartikey Link: https://syzkaller.appspot.com/bug?extid=6a680377e13041c19d50 Link: https://patch.msgid.link/20260621035841.56194-1-kartikey406@gmail.com Signed-off-by: Jan Kara --- fs/udf/balloc.c | 12 ++++++++++-- fs/udf/inode.c | 19 ++++++++++++++++--- fs/udf/truncate.c | 2 +- fs/udf/udfdecl.h | 3 ++- 4 files changed, 29 insertions(+), 7 deletions(-) diff --git a/fs/udf/balloc.c b/fs/udf/balloc.c index cc6dc6e1d84d..30cec5600149 100644 --- a/fs/udf/balloc.c +++ b/fs/udf/balloc.c @@ -502,6 +502,8 @@ static int udf_table_prealloc_blocks(struct super_block *sb, int8_t etype = -1; struct udf_inode_info *iinfo; int ret = 0; + /* AED block freed by udf_delete_aext(), released after unlock */ + struct kernel_lb_addr freed = { .partitionReferenceNum = 0xFFFF }; if (first_block >= sbi->s_partmaps[partition].s_partition_len) return 0; @@ -541,7 +543,7 @@ static int udf_table_prealloc_blocks(struct super_block *sb, udf_write_aext(table, &epos, &eloc, (etype << 30) | elen, 1); } else - udf_delete_aext(table, epos); + udf_delete_aext(table, epos, &freed); } else { alloc_count = 0; } @@ -552,6 +554,8 @@ static int udf_table_prealloc_blocks(struct super_block *sb, if (alloc_count) udf_add_free_space(sb, partition, -alloc_count); mutex_unlock(&sbi->s_alloc_mutex); + if (freed.partitionReferenceNum != 0xFFFF) + udf_free_blocks(sb, table, &freed, 0, 1); return alloc_count; } @@ -560,6 +564,8 @@ static udf_pblk_t udf_table_new_block(struct super_block *sb, uint32_t goal, int *err) { struct udf_sb_info *sbi = UDF_SB(sb); + /* AED block freed by udf_delete_aext(), released after unlock */ + struct kernel_lb_addr freed = { .partitionReferenceNum = 0xFFFF }; uint32_t spread = 0xFFFFFFFF, nspread = 0xFFFFFFFF; udf_pblk_t newblock = 0; uint32_t adsize; @@ -643,12 +649,14 @@ static udf_pblk_t udf_table_new_block(struct super_block *sb, if (goal_elen) udf_write_aext(table, &goal_epos, &goal_eloc, goal_elen, 1); else - udf_delete_aext(table, goal_epos); + udf_delete_aext(table, goal_epos, &freed); brelse(goal_epos.bh); udf_add_free_space(sb, partition, -1); mutex_unlock(&sbi->s_alloc_mutex); + if (freed.partitionReferenceNum != 0xFFFF) + udf_free_blocks(sb, table, &freed, 0, 1); *err = 0; return newblock; } diff --git a/fs/udf/inode.c b/fs/udf/inode.c index c4a08e8bc1c9..c97914aa8d8b 100644 --- a/fs/udf/inode.c +++ b/fs/udf/inode.c @@ -1204,7 +1204,7 @@ static int udf_update_extents(struct inode *inode, struct kernel_long_ad *laarr, if (startnum > endnum) { for (i = 0; i < (startnum - endnum); i++) - udf_delete_aext(inode, *epos); + udf_delete_aext(inode, *epos, NULL); } else if (startnum < endnum) { for (i = 0; i < (endnum - startnum); i++) { err = udf_insert_aext(inode, *epos, @@ -2335,7 +2335,8 @@ static int udf_insert_aext(struct inode *inode, struct extent_position epos, return ret; } -int8_t udf_delete_aext(struct inode *inode, struct extent_position epos) +int8_t udf_delete_aext(struct inode *inode, struct extent_position epos, + struct kernel_lb_addr *freed) { struct extent_position oepos; int adsize; @@ -2385,7 +2386,19 @@ int8_t udf_delete_aext(struct inode *inode, struct extent_position epos) elen = 0; if (epos.bh != oepos.bh) { - udf_free_blocks(inode->i_sb, inode, &epos.block, 0, 1); + /* + * The block that held the now-empty allocation extent must be + * returned to free space. When the caller already holds + * s_alloc_mutex (the space-table allocator in balloc.c), + * freeing it inline would recurse through udf_free_blocks() + * into udf_table_free_blocks() and deadlock re-acquiring + * s_alloc_mutex. In that case report the block to the caller, + * which frees it after dropping the lock. + */ + if (freed) + *freed = epos.block; + else + udf_free_blocks(inode->i_sb, inode, &epos.block, 0, 1); udf_write_aext(inode, &oepos, &eloc, elen, 1); udf_write_aext(inode, &oepos, &eloc, elen, 1); if (!oepos.bh) { diff --git a/fs/udf/truncate.c b/fs/udf/truncate.c index 41b2bfd30449..0990f94b8551 100644 --- a/fs/udf/truncate.c +++ b/fs/udf/truncate.c @@ -159,7 +159,7 @@ void udf_discard_prealloc(struct inode *inode) if (etype == (EXT_NOT_RECORDED_ALLOCATED >> 30)) { lbcount -= elen; - udf_delete_aext(inode, prev_epos); + udf_delete_aext(inode, prev_epos, NULL); udf_free_blocks(inode->i_sb, inode, &eloc, 0, DIV_ROUND_UP(elen, bsize)); } diff --git a/fs/udf/udfdecl.h b/fs/udf/udfdecl.h index 6d951e05c004..21de6925fc68 100644 --- a/fs/udf/udfdecl.h +++ b/fs/udf/udfdecl.h @@ -170,7 +170,8 @@ extern int udf_add_aext(struct inode *, struct extent_position *, struct kernel_lb_addr *, uint32_t, int); extern void udf_write_aext(struct inode *, struct extent_position *, struct kernel_lb_addr *, uint32_t, int); -extern int8_t udf_delete_aext(struct inode *, struct extent_position); +extern int8_t udf_delete_aext(struct inode *, struct extent_position, + struct kernel_lb_addr *); extern int udf_next_aext(struct inode *inode, struct extent_position *epos, struct kernel_lb_addr *eloc, uint32_t *elen, int8_t *etype, int inc);