From 3a2d040070df33176e0cd0894f5fc8bf89089b7e Mon Sep 17 00:00:00 2001 From: Qu Wenruo Date: Tue, 24 Mar 2020 11:08:55 +0800 Subject: [PATCH] btrfs-progs: check/lowmem: Fix access on uninitialized memory [BUG] There are some reports on fsck/001 test segfault failure with lowmem mode. While I failed to reproduce it, valgrind still catches it with the following output: Delete backref in extent [12845056 1048576] ERROR: file extent [257, 0] has unaligned disk bytenr: 755944791, should be aligned to 4096 ERROR: file extent[257 0] root 5 owner 5 backref lost Deleted root 5 item[257, 108, 0] ==29080== Conditional jump or move depends on uninitialised value(s) ==29080== at 0x1A81D7: btrfs_release_path (ctree.c:97) ==29080== by 0x192C33: repair_extent_data_item (mode-lowmem.c:3330) ==29080== by 0x1962FF: check_leaf_items (mode-lowmem.c:4696) ==29080== by 0x196ABF: walk_down_tree (mode-lowmem.c:4858) ==29080== by 0x197762: check_btrfs_root (mode-lowmem.c:5157) ==29080== by 0x198335: check_chunks_and_extents_lowmem (mode-lowmem.c:5450) ==29080== by 0x166414: do_check_chunks_and_extents (main.c:8829) ==29080== by 0x169CF7: cmd_check (main.c:10313) ==29080== by 0x11CDC6: cmd_execute (commands.h:125) ==29080== by 0x11D712: main (btrfs.c:386) ==29080== [CAUSE] In repair_extent_data_item() if we find unaligned file extent, we just delete it and kick in hole punch procedure. The problem is, file extent deletion is done before initializing @path. And when the deletion is done without problem, we will goto out tag, which will release @path, containing uninitialized values, and triggering segfault. [FIX] Don't try to abort trans nor free path if we're going through file extent deletion routine. Fixes: 0617bde3bc15 ("btrfs-progs: lowmem: delete unaligned bytes extent data under repair") Signed-off-by: Qu Wenruo Signed-off-by: David Sterba --- check/mode-lowmem.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/check/mode-lowmem.c b/check/mode-lowmem.c index 1d2df349..113ee619 100644 --- a/check/mode-lowmem.c +++ b/check/mode-lowmem.c @@ -3257,7 +3257,7 @@ static int repair_extent_data_item(struct btrfs_root *root, ret = delete_item(root, pathp); if (!ret) err = 0; - goto out; + goto out_no_release; } /* now repair only adds backref */ @@ -3332,6 +3332,7 @@ out: if (trans) btrfs_commit_transaction(trans, root); btrfs_release_path(&path); +out_no_release: if (ret) error("can't repair root %llu extent data item[%llu %llu]", root->objectid, disk_bytenr, num_bytes);