Patch "ext4: fix slab-use-after-free in ext4_es_insert_extent()" has been added to the 6.1-stable tree

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This is a note to let you know that I've just added the patch titled

    ext4: fix slab-use-after-free in ext4_es_insert_extent()

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ext4-fix-slab-use-after-free-in-ext4_es_insert_exten.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit ac45c2099e6af9400b454ef68cb56517a584f345
Author: Baokun Li <libaokun1@xxxxxxxxxx>
Date:   Tue Aug 15 15:08:08 2023 +0800

    ext4: fix slab-use-after-free in ext4_es_insert_extent()
    
    [ Upstream commit 768d612f79822d30a1e7d132a4d4b05337ce42ec ]
    
    Yikebaer reported an issue:
    ==================================================================
    BUG: KASAN: slab-use-after-free in ext4_es_insert_extent+0xc68/0xcb0
    fs/ext4/extents_status.c:894
    Read of size 4 at addr ffff888112ecc1a4 by task syz-executor/8438
    
    CPU: 1 PID: 8438 Comm: syz-executor Not tainted 6.5.0-rc5 #1
    Call Trace:
     [...]
     kasan_report+0xba/0xf0 mm/kasan/report.c:588
     ext4_es_insert_extent+0xc68/0xcb0 fs/ext4/extents_status.c:894
     ext4_map_blocks+0x92a/0x16f0 fs/ext4/inode.c:680
     ext4_alloc_file_blocks.isra.0+0x2df/0xb70 fs/ext4/extents.c:4462
     ext4_zero_range fs/ext4/extents.c:4622 [inline]
     ext4_fallocate+0x251c/0x3ce0 fs/ext4/extents.c:4721
     [...]
    
    Allocated by task 8438:
     [...]
     kmem_cache_zalloc include/linux/slab.h:693 [inline]
     __es_alloc_extent fs/ext4/extents_status.c:469 [inline]
     ext4_es_insert_extent+0x672/0xcb0 fs/ext4/extents_status.c:873
     ext4_map_blocks+0x92a/0x16f0 fs/ext4/inode.c:680
     ext4_alloc_file_blocks.isra.0+0x2df/0xb70 fs/ext4/extents.c:4462
     ext4_zero_range fs/ext4/extents.c:4622 [inline]
     ext4_fallocate+0x251c/0x3ce0 fs/ext4/extents.c:4721
     [...]
    
    Freed by task 8438:
     [...]
     kmem_cache_free+0xec/0x490 mm/slub.c:3823
     ext4_es_try_to_merge_right fs/ext4/extents_status.c:593 [inline]
     __es_insert_extent+0x9f4/0x1440 fs/ext4/extents_status.c:802
     ext4_es_insert_extent+0x2ca/0xcb0 fs/ext4/extents_status.c:882
     ext4_map_blocks+0x92a/0x16f0 fs/ext4/inode.c:680
     ext4_alloc_file_blocks.isra.0+0x2df/0xb70 fs/ext4/extents.c:4462
     ext4_zero_range fs/ext4/extents.c:4622 [inline]
     ext4_fallocate+0x251c/0x3ce0 fs/ext4/extents.c:4721
     [...]
    ==================================================================
    
    The flow of issue triggering is as follows:
    1. remove es
          raw es               es  removed  es1
    |-------------------| -> |----|.......|------|
    
    2. insert es
      es   insert   es1      merge with es  es1     merge with es and free es1
    |----|.......|------| -> |------------|------| -> |-------------------|
    
    es merges with newes, then merges with es1, frees es1, then determines
    if es1->es_len is 0 and triggers a UAF.
    
    The code flow is as follows:
    ext4_es_insert_extent
      es1 = __es_alloc_extent(true);
      es2 = __es_alloc_extent(true);
      __es_remove_extent(inode, lblk, end, NULL, es1)
        __es_insert_extent(inode, &newes, es1) ---> insert es1 to es tree
      __es_insert_extent(inode, &newes, es2)
        ext4_es_try_to_merge_right
          ext4_es_free_extent(inode, es1) --->  es1 is freed
      if (es1 && !es1->es_len)
        // Trigger UAF by determining if es1 is used.
    
    We determine whether es1 or es2 is used immediately after calling
    __es_remove_extent() or __es_insert_extent() to avoid triggering a
    UAF if es1 or es2 is freed.
    
    Reported-by: Yikebaer Aizezi <yikebaer61@xxxxxxxxx>
    Closes: https://lore.kernel.org/lkml/CALcu4raD4h9coiyEBL4Bm0zjDwxC2CyPiTwsP3zFuhot6y9Beg@xxxxxxxxxxxxxx
    Fixes: 2a69c450083d ("ext4: using nofail preallocation in ext4_es_insert_extent()")
    Cc: stable@xxxxxxxxxx
    Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
    Reviewed-by: Jan Kara <jack@xxxxxxx>
    Link: https://lore.kernel.org/r/20230815070808.3377171-1-libaokun1@xxxxxxxxxx
    Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
    Stable-dep-of: 8e387c89e96b ("ext4: make sure allocate pending entry not fail")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
index 934c14f9edb9f..e8533b4f891bf 100644
--- a/fs/ext4/extents_status.c
+++ b/fs/ext4/extents_status.c
@@ -882,23 +882,29 @@ int ext4_es_insert_extent(struct inode *inode, ext4_lblk_t lblk,
 	err1 = __es_remove_extent(inode, lblk, end, NULL, es1);
 	if (err1 != 0)
 		goto error;
+	/* Free preallocated extent if it didn't get used. */
+	if (es1) {
+		if (!es1->es_len)
+			__es_free_extent(es1);
+		es1 = NULL;
+	}
 
 	err2 = __es_insert_extent(inode, &newes, es2);
 	if (err2 == -ENOMEM && !ext4_es_must_keep(&newes))
 		err2 = 0;
 	if (err2 != 0)
 		goto error;
+	/* Free preallocated extent if it didn't get used. */
+	if (es2) {
+		if (!es2->es_len)
+			__es_free_extent(es2);
+		es2 = NULL;
+	}
 
 	if (sbi->s_cluster_ratio > 1 && test_opt(inode->i_sb, DELALLOC) &&
 	    (status & EXTENT_STATUS_WRITTEN ||
 	     status & EXTENT_STATUS_UNWRITTEN))
 		__revise_pending(inode, lblk, len);
-
-	/* es is pre-allocated but not used, free it. */
-	if (es1 && !es1->es_len)
-		__es_free_extent(es1);
-	if (es2 && !es2->es_len)
-		__es_free_extent(es2);
 error:
 	write_unlock(&EXT4_I(inode)->i_es_lock);
 	if (err1 || err2)
@@ -1495,8 +1501,12 @@ int ext4_es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
 	 */
 	write_lock(&EXT4_I(inode)->i_es_lock);
 	err = __es_remove_extent(inode, lblk, end, &reserved, es);
-	if (es && !es->es_len)
-		__es_free_extent(es);
+	/* Free preallocated extent if it didn't get used. */
+	if (es) {
+		if (!es->es_len)
+			__es_free_extent(es);
+		es = NULL;
+	}
 	write_unlock(&EXT4_I(inode)->i_es_lock);
 	if (err)
 		goto retry;
@@ -2055,19 +2065,25 @@ int ext4_es_insert_delayed_block(struct inode *inode, ext4_lblk_t lblk,
 	err1 = __es_remove_extent(inode, lblk, lblk, NULL, es1);
 	if (err1 != 0)
 		goto error;
+	/* Free preallocated extent if it didn't get used. */
+	if (es1) {
+		if (!es1->es_len)
+			__es_free_extent(es1);
+		es1 = NULL;
+	}
 
 	err2 = __es_insert_extent(inode, &newes, es2);
 	if (err2 != 0)
 		goto error;
+	/* Free preallocated extent if it didn't get used. */
+	if (es2) {
+		if (!es2->es_len)
+			__es_free_extent(es2);
+		es2 = NULL;
+	}
 
 	if (allocated)
 		__insert_pending(inode, lblk);
-
-	/* es is pre-allocated but not used, free it. */
-	if (es1 && !es1->es_len)
-		__es_free_extent(es1);
-	if (es2 && !es2->es_len)
-		__es_free_extent(es2);
 error:
 	write_unlock(&EXT4_I(inode)->i_es_lock);
 	if (err1 || err2)



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