btrfs: fix invalid leaf access due to inline extent during lseek

During lseek, for SEEK_DATA and SEEK_HOLE modes, we access the disk_bytenr
of an extent without checking its type. However inline extents have their
data starting the offset of the disk_bytenr field, so accessing that field
when we have an inline extent can result in either of the following:

1) Interpret the inline extent's data as a disk_bytenr value;

2) In case the inline data is less than 8 bytes, we access part of some
   other item in the leaf, or unused space in the leaf;

3) In case the inline data is less than 8 bytes and the extent item is
   the first item in the leaf, we can access beyond the leaf's limit.

So fix this by not accessing the disk_bytenr field if we have an inline
extent.

Fixes: b6e833567ea1 ("btrfs: make hole and data seeking a lot more efficient")
Reported-by: Matthias Schoepfer <matthias.schoepfer@googlemail.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=216908
Link: https://lore.kernel.org/linux-btrfs/7f25442f-b121-2a3a-5a3d-22bcaae83cd4@leemhuis.info/
CC: stable@vger.kernel.org # 6.1
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 834bbcb..af046d2 100644 (file)
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -3541,6 +3541,7 @@ static loff_t find_desired_extent(struct file *file, loff_t offset, int whence)
                struct extent_buffer *leaf = path->nodes[0];
                struct btrfs_file_extent_item *extent;
                u64 extent_end;
+               u8 type;
 
                if (path->slots[0] >= btrfs_header_nritems(leaf)) {
                        ret = btrfs_next_leaf(root, path);
@@ -3596,10 +3597,16 @@ static loff_t find_desired_extent(struct file *file, loff_t offset, int whence)
 
                extent = btrfs_item_ptr(leaf, path->slots[0],
                                        struct btrfs_file_extent_item);
+               type = btrfs_file_extent_type(leaf, extent);
 
-               if (btrfs_file_extent_disk_bytenr(leaf, extent) == 0 ||
-                   btrfs_file_extent_type(leaf, extent) ==
-                   BTRFS_FILE_EXTENT_PREALLOC) {
+               /*
+                * Can't access the extent's disk_bytenr field if this is an
+                * inline extent, since at that offset, it's where the extent
+                * data starts.
+                */
+               if (type == BTRFS_FILE_EXTENT_PREALLOC ||
+                   (type == BTRFS_FILE_EXTENT_REG &&
+                    btrfs_file_extent_disk_bytenr(leaf, extent) == 0)) {
                        /*
                         * Explicit hole or prealloc extent, search for delalloc.
                         * A prealloc extent is treated like a hole.