From: Baokun Li <libaokun1@xxxxxxxxxx>
As Ojaswin mentioned in Link, in ext4_ext_insert_extent(), if the path is
reallocated in ext4_ext_create_new_leaf(), we'll use the stale path and
cause UAF. Below is a sample trace with dummy values:
ext4_ext_insert_extent
path = *ppath = 2000
ext4_ext_create_new_leaf(ppath)
ext4_find_extent(ppath)
path = *ppath = 2000
if (depth > path[0].p_maxdepth)
kfree(path = 2000);
*ppath = path = NULL;
path = kcalloc() = 3000
*ppath = 3000;
return path;
/* here path is still 2000, UAF! */
eh = path[depth].p_hdr
==================================================================
BUG: KASAN: slab-use-after-free in ext4_ext_insert_extent+0x26d4/0x3330
Read of size 8 at addr ffff8881027bf7d0 by task kworker/u36:1/179
CPU: 3 UID: 0 PID: 179 Comm: kworker/u6:1 Not tainted 6.11.0-rc2-dirty #866
Call Trace:
<TASK>
ext4_ext_insert_extent+0x26d4/0x3330
ext4_ext_map_blocks+0xe22/0x2d40
ext4_map_blocks+0x71e/0x1700
ext4_do_writepages+0x1290/0x2800
[...]
Allocated by task 179:
ext4_find_extent+0x81c/0x1f70
ext4_ext_map_blocks+0x146/0x2d40
ext4_map_blocks+0x71e/0x1700
ext4_do_writepages+0x1290/0x2800
ext4_writepages+0x26d/0x4e0
do_writepages+0x175/0x700
[...]
Freed by task 179:
kfree+0xcb/0x240
ext4_find_extent+0x7c0/0x1f70
ext4_ext_insert_extent+0xa26/0x3330
ext4_ext_map_blocks+0xe22/0x2d40
ext4_map_blocks+0x71e/0x1700
ext4_do_writepages+0x1290/0x2800
ext4_writepages+0x26d/0x4e0
do_writepages+0x175/0x700
[...]
==================================================================
So use *ppath to update the path to avoid the above problem.
Reported-by: Ojaswin Mujoo <ojaswin@xxxxxxxxxxxxx>
Closes: https://lore.kernel.org/r/ZqyL6rmtwl6N4MWR@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 10809df84a4d ("ext4: teach ext4_ext_find_extent() to realloc path if necessary")
Cc: stable@xxxxxxxxxx
Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
---
fs/ext4/extents.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 5879aef159d8..91c6586afcca 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -2116,6 +2116,7 @@ int ext4_ext_insert_extent(handle_t *handle, struct inode *inode,
ppath, newext);
if (err)
goto cleanup;
+ path = *ppath;
depth = ext_depth(inode);
eh = path[depth].p_hdr;
--
2.39.2
