ext4: update orig_path in ext4_find_extent()

commit 5b4b2dcace35f618fe361a87bae6f0d13af31bc1 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index e5500c4e8c9398083572cd454e140747cf361f57..c64f7c1b1d9082602be19a333f03ce0f8717bb1b 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:
@@ -3249,7 +3251,6 @@ 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 204f53b236229fbb18b8695ee29f333c41a4f01e..c95e3e526390d79bf95f3adc5f31ce516d57888f 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;
 }