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btrfs: fix extent map use-after-free when adding pages to compressed bio

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At add_ra_bio_pages() we are accessing the extent map to calculate
'add_size' after we dropped our reference on the extent map, resulting
in a use-after-free. Fix this by computing 'add_size' before dropping our
extent map reference.

Reported-by: syzbot+853d80cba98ce1157ae6@syzkaller.appspotmail.com
Link: https://lore.kernel.org/linux-btrfs/000000000000038144061c6d18f2@google.com/
Fixes: 6a4049102055 ("btrfs: subpage: make add_ra_bio_pages() compatible")
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>
This commit is contained in:
Filipe Manana 2024-07-04 16:11:20 +01:00 committed by David Sterba
parent 320d8dc612
commit 8e7860543a
1 changed files with 1 additions and 1 deletions
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2
fs/btrfs/compression.c
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@ -515,6 +515,7 @@ static noinline int add_ra_bio_pages(struct inode *inode,
put_page(page); put_page(page);
break; break;
} }
add_size = min(em->start + em->len, page_end + 1) - cur;
free_extent_map(em); free_extent_map(em);
if (page->index == end_index) { if (page->index == end_index) {
@ -527,7 +528,6 @@ static noinline int add_ra_bio_pages(struct inode *inode,
} }
} }
add_size = min(em->start + em->len, page_end + 1) - cur;
ret = bio_add_page(orig_bio, page, add_size, offset_in_page(cur)); ret = bio_add_page(orig_bio, page, add_size, offset_in_page(cur));
if (ret != add_size) { if (ret != add_size) {
unlock_extent(tree, cur, page_end, NULL); unlock_extent(tree, cur, page_end, NULL);