ext4: update orig_path in ext4_find_extent()

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>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20240822023545.1994557-6-libaokun@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index caef913565570c7994be502b4d7b920d3a0df18a..c8e7676f6af908a0f38f1391edae472703819ee8 100644 (file)
--- 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 516897b0218e3367fd8a743c701da171c4d3f4c5..228b56f7d0475a8e5c03816adeb63481c7ec73c5 100644 (file)
--- 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;
 }