6.6-stable review patch. If anyone has any objections, please let me know.
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From: Baokun Li libaokun1@huawei.com
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 --- fs/ext4/extents.c | 3 ++- fs/ext4/move_extent.c | 1 - 2 files changed, 2 insertions(+), 2 deletions(-)
--- a/fs/ext4/extents.c +++ b/fs/ext4/extents.c @@ -957,6 +957,8 @@ ext4_find_extent(struct inode *inode, ex
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 } 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)) { --- a/fs/ext4/move_extent.c +++ b/fs/ext4/move_extent.c @@ -36,7 +36,6 @@ get_ext_path(struct inode *inode, ext4_l *ppath = NULL; return -ENODATA; } - *ppath = path; return 0; }