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authorQu Wenruo <wqu@suse.com>2020-07-28 11:39:26 +0300
committerDavid Sterba <dsterba@suse.com>2020-08-10 19:57:59 +0300
commit1e6e238c3002ea3611465ce5f32777ddd6a40126 (patch)
tree9563ca4536d509bc2bc2e0b36b1c70f22622fd85 /fs/btrfs
parent5e548b32018d96c377fda4bdac2bf511a448ca67 (diff)
downloadlinux-1e6e238c3002ea3611465ce5f32777ddd6a40126.tar.xz
btrfs: inode: fix NULL pointer dereference if inode doesn't need compression
[BUG] There is a bug report of NULL pointer dereference caused in compress_file_extent(): Oops: Kernel access of bad area, sig: 11 [#1] LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries Workqueue: btrfs-delalloc btrfs_delalloc_helper [btrfs] NIP [c008000006dd4d34] compress_file_range.constprop.41+0x75c/0x8a0 [btrfs] LR [c008000006dd4d1c] compress_file_range.constprop.41+0x744/0x8a0 [btrfs] Call Trace: [c000000c69093b00] [c008000006dd4d1c] compress_file_range.constprop.41+0x744/0x8a0 [btrfs] (unreliable) [c000000c69093bd0] [c008000006dd4ebc] async_cow_start+0x44/0xa0 [btrfs] [c000000c69093c10] [c008000006e14824] normal_work_helper+0xdc/0x598 [btrfs] [c000000c69093c80] [c0000000001608c0] process_one_work+0x2c0/0x5b0 [c000000c69093d10] [c000000000160c38] worker_thread+0x88/0x660 [c000000c69093db0] [c00000000016b55c] kthread+0x1ac/0x1c0 [c000000c69093e20] [c00000000000b660] ret_from_kernel_thread+0x5c/0x7c ---[ end trace f16954aa20d822f6 ]--- [CAUSE] For the following execution route of compress_file_range(), it's possible to hit NULL pointer dereference: compress_file_extent() |- pages = NULL; |- start = async_chunk->start = 0; |- end = async_chunk = 4095; |- nr_pages = 1; |- inode_need_compress() == false; <<< Possible, see later explanation | Now, we have nr_pages = 1, pages = NULL |- cont: |- ret = cow_file_range_inline(); |- if (ret <= 0) { |- for (i = 0; i < nr_pages; i++) { |- WARN_ON(pages[i]->mapping); <<< Crash To enter above call execution branch, we need the following race: Thread 1 (chattr) | Thread 2 (writeback) --------------------------+------------------------------ | btrfs_run_delalloc_range | |- inode_need_compress = true | |- cow_file_range_async() btrfs_ioctl_set_flag() | |- binode_flags |= | BTRFS_INODE_NOCOMPRESS | | compress_file_range() | |- inode_need_compress = false | |- nr_page = 1 while pages = NULL | | Then hit the crash [FIX] This patch will fix it by checking @pages before doing accessing it. This patch is only designed as a hot fix and easy to backport. More elegant fix may make btrfs only check inode_need_compress() once to avoid such race, but that would be another story. Reported-by: Luciano Chavez <chavez@us.ibm.com> Fixes: 4d3a800ebb12 ("btrfs: merge nr_pages input and output parameter in compress_pages") CC: stable@vger.kernel.org # 4.14.x: cecc8d9038d16: btrfs: Move free_pages_out label in inline extent handling branch in compress_file_range CC: stable@vger.kernel.org # 4.14+ Signed-off-by: Qu Wenruo <wqu@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs/btrfs')
-rw-r--r--fs/btrfs/inode.c16
1 files changed, 11 insertions, 5 deletions
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 611b3412fbfd..9988d754e465 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -653,12 +653,18 @@ cont:
page_error_op |
PAGE_END_WRITEBACK);
- for (i = 0; i < nr_pages; i++) {
- WARN_ON(pages[i]->mapping);
- put_page(pages[i]);
+ /*
+ * Ensure we only free the compressed pages if we have
+ * them allocated, as we can still reach here with
+ * inode_need_compress() == false.
+ */
+ if (pages) {
+ for (i = 0; i < nr_pages; i++) {
+ WARN_ON(pages[i]->mapping);
+ put_page(pages[i]);
+ }
+ kfree(pages);
}
- kfree(pages);
-
return 0;
}
}