[PATCH v2 05/25] ext4: update orig_path in ext4_find_extent()

libaokun
2024-08-22T02:40:36Z

In ext4_find_extent(), if the path is not big enough, we free it and set
*orig_path to NULL. But after reallocating and successfully initializing
the path, we don't update *orig_path, in which case the caller gets a
valid path but a NULL ppath, and this may cause a NULL pointer dereference
or a path memory leak. For example:

ext4_split_extent
path = *ppath = 2000
ext4_find_extent
if (depth > path[0].p_maxdepth)
kfree(path = 2000);
*orig_path = path = NULL;
path = kcalloc() = 3000
ext4_split_extent_at(*ppath = NULL)
path = *ppath;
ex = path[depth].p_ext;
// NULL pointer dereference!

==================================================================
BUG: kernel NULL pointer dereference, address: 0000000000000010
CPU: 6 UID: 0 PID: 576 Comm: fsstress Not tainted 6.11.0-rc2-dirty #847
RIP: 0010:ext4_split_extent_at+0x6d/0x560
Call Trace:
<TASK>
ext4_split_extent.isra.0+0xcb/0x1b0
ext4_ext_convert_to_initialized+0x168/0x6c0
ext4_ext_handle_unwritten_extents+0x325/0x4d0
ext4_ext_map_blocks+0x520/0xdb0
ext4_map_blocks+0x2b0/0x690
ext4_iomap_begin+0x20e/0x2c0
[...]
==================================================================

Therefore, *orig_path is updated when the extent lookup succeeds, so that
the caller can safely use path or *ppath.

Fixes: 10809df84a4d ("ext4: teach ext4_ext_find_extent() to realloc path if necessary")
Cc: stable@kernel.org
Signed-off-by: Baokun Li <libaokun1@huawei.com>
---
fs/ext4/extents.c | 3 ++-
fs/ext4/move_extent.c | 1 -
2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 0224cf0ef19e..5879aef159d8 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -957,6 +957,8 @@ ext4_find_extent(struct inode *inode, ext4_lblk_t block,

ext4_ext_show_path(inode, path);

+ if (orig_path)
+ *orig_path = path;
return path;

err:
@@ -3268,7 +3270,6 @@ static int ext4_split_extent_at(handle_t *handle,
}
depth = ext_depth(inode);
ex = path[depth].p_ext;
- *ppath = path;

if (EXT4_EXT_MAY_ZEROOUT & split_flag) {
if (split_flag & (EXT4_EXT_DATA_VALID1|EXT4_EXT_DATA_VALID2)) {
diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
index 204f53b23622..c95e3e526390 100644
--- a/fs/ext4/move_extent.c
+++ b/fs/ext4/move_extent.c
@@ -36,7 +36,6 @@ get_ext_path(struct inode *inode, ext4_lblk_t lblock,
*ppath = NULL;
return -ENODATA;
}
- *ppath = path;
return 0;
}

--
2.39.2