From 2a527d6858c246db8afc3d576dbcbff0902f933b Mon Sep 17 00:00:00 2001 From: Alexander Potapenko Date: Wed, 5 Jul 2017 00:56:21 -0400 Subject: [PATCH] fs: generic_block_bmap(): initialize all of the fields in the temp bh KMSAN (KernelMemorySanitizer, a new error detection tool) reports the use of uninitialized memory in ext4_update_bh_state(): ================================================================== BUG: KMSAN: use of unitialized memory CPU: 3 PID: 1 Comm: swapper/0 Tainted: G B 4.8.0-rc6+ #597 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 0000000000000282 ffff88003cc96f68 ffffffff81f30856 0000003000000008 ffff88003cc96f78 0000000000000096 ffffffff8169742a ffff88003cc96ff8 ffffffff812fc1fc 0000000000000008 ffff88003a1980e8 0000000100000000 Call Trace: [< inline >] __dump_stack lib/dump_stack.c:15 [] dump_stack+0xa6/0xc0 lib/dump_stack.c:51 [] kmsan_report+0x1ec/0x300 mm/kmsan/kmsan.c:? [] __msan_warning+0x2b/0x40 ??:? [< inline >] ext4_update_bh_state fs/ext4/inode.c:727 [] _ext4_get_block+0x6ca/0x8a0 fs/ext4/inode.c:759 [] ext4_get_block+0x8c/0xa0 fs/ext4/inode.c:769 [] generic_block_bmap+0x246/0x2b0 fs/buffer.c:2991 [] ext4_bmap+0x5ee/0x660 fs/ext4/inode.c:3177 ... origin description: ----tmp@generic_block_bmap ================================================================== (the line numbers are relative to 4.8-rc6, but the bug persists upstream) The local |tmp| is created in generic_block_bmap() and then passed into ext4_bmap() => ext4_get_block() => _ext4_get_block() => ext4_update_bh_state(). Along the way tmp.b_page is never initialized before ext4_update_bh_state() checks its value. [ Use the approach suggested by Kees Cook of initializing the whole bh structure.] Signed-off-by: Alexander Potapenko Signed-off-by: Theodore Ts'o --- fs/buffer.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/fs/buffer.c b/fs/buffer.c index 161be58c5cb0..a3399aa6a2bd 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -3021,11 +3021,11 @@ EXPORT_SYMBOL(block_write_full_page); sector_t generic_block_bmap(struct address_space *mapping, sector_t block, get_block_t *get_block) { - struct buffer_head tmp; struct inode *inode = mapping->host; - tmp.b_state = 0; - tmp.b_blocknr = 0; - tmp.b_size = i_blocksize(inode); + struct buffer_head tmp = { + .b_size = i_blocksize(inode), + }; + get_block(inode, block, &tmp, 0); return tmp.b_blocknr; } -- GitLab