[PATCH] btrfs: fix a out-of-boundary access for copy_compressed_data_to_page()
From: Qu Wenruo <hidden>
Date: 2021-11-12 02:23:15
[BUG]
The following script can cause btrfs to crash:
mount -o compress-force=lzo $DEV /mnt
dd if=/dev/urandom of=/mnt/foo bs=4k count=1
sync
The calltrace looks like this:
general protection fault, probably for non-canonical address 0xe04b37fccce3b000: 0000 [#1] PREEMPT SMP NOPTI
CPU: 5 PID: 164 Comm: kworker/u20:3 Not tainted 5.15.0-rc7-custom+ #4
Workqueue: btrfs-delalloc btrfs_work_helper [btrfs]
RIP: 0010:__memcpy+0x12/0x20
Call Trace:
lzo_compress_pages+0x236/0x540 [btrfs]
btrfs_compress_pages+0xaa/0xf0 [btrfs]
compress_file_range+0x431/0x8e0 [btrfs]
async_cow_start+0x12/0x30 [btrfs]
btrfs_work_helper+0xf6/0x3e0 [btrfs]
process_one_work+0x294/0x5d0
worker_thread+0x55/0x3c0
kthread+0x140/0x170
ret_from_fork+0x22/0x30
---[ end trace 63c3c0f131e61982 ]---
[CAUSE]
In lzo_compress_pages(), parameter @out_pages is not only an output
parameter (for the compressed pages), but also an input parameter, for
the maximum amount of pages we can utilize.
In commit d4088803f511 ("btrfs: subpage: make lzo_compress_pages()
compatible"), the refactor doesn't take @out_pages as an input, thus
completely ignoring the limit.
And for compress-force case, we could hit incompressible data that
compressed size would go beyond the page limit, and cause above crash.
[FIX]
Save @out_pages as @max_nr_page, and pass it to lzo_compress_pages(),
and check if we're beyond the limit before accessing the pages.
Reported-by: Omar Sandoval <redacted>
Fixes: d4088803f511 ("btrfs: subpage: make lzo_compress_pages() compatible")
Signed-off-by: Qu Wenruo <redacted>
---
fs/btrfs/lzo.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/lzo.c b/fs/btrfs/lzo.c
index 00cffc183ec0..f410ceabcdbd 100644
--- a/fs/btrfs/lzo.c
+++ b/fs/btrfs/lzo.c@@ -125,6 +125,7 @@ static inline size_t read_compress_length(const char *buf) static int copy_compressed_data_to_page(char *compressed_data, size_t compressed_size, struct page **out_pages, + unsigned long max_nr_page, u32 *cur_out, const u32 sectorsize) {
@@ -132,6 +133,9 @@ static int copy_compressed_data_to_page(char *compressed_data, u32 orig_out; struct page *cur_page; + if ((*cur_out / PAGE_SIZE) >= max_nr_page) + return -E2BIG; + /* * We never allow a segment header crossing sector boundary, previous * run should ensure we have enough space left inside the sector.
@@ -158,6 +162,9 @@ static int copy_compressed_data_to_page(char *compressed_data, u32 copy_len = min_t(u32, sectorsize - *cur_out % sectorsize, orig_out + compressed_size - *cur_out); + if ((*cur_out / PAGE_SIZE) >= max_nr_page) + return -E2BIG; + cur_page = out_pages[*cur_out / PAGE_SIZE]; /* Allocate a new page */ if (!cur_page) {
@@ -195,6 +202,7 @@ int lzo_compress_pages(struct list_head *ws, struct address_space *mapping, struct workspace *workspace = list_entry(ws, struct workspace, list); const u32 sectorsize = btrfs_sb(mapping->host->i_sb)->sectorsize; struct page *page_in = NULL; + const unsigned long max_nr_page = *out_pages; int ret = 0; /* Points to the file offset of input data */ u64 cur_in = start;
@@ -202,6 +210,7 @@ int lzo_compress_pages(struct list_head *ws, struct address_space *mapping, u32 cur_out = 0; u32 len = *total_out; + ASSERT(max_nr_page > 0); *out_pages = 0; *total_out = 0; *total_in = 0;
@@ -237,7 +246,8 @@ int lzo_compress_pages(struct list_head *ws, struct address_space *mapping, } ret = copy_compressed_data_to_page(workspace->cbuf, out_len, - pages, &cur_out, sectorsize); + pages, max_nr_page, + &cur_out, sectorsize); if (ret < 0) goto out;
--
2.33.1