123 lines
3.7 KiB
Diff
123 lines
3.7 KiB
Diff
From 99d63b3e3be79190d3bb4759bfb3a47fd00cfdbe Mon Sep 17 00:00:00 2001
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From: Sungjong Seo <sj1557.seo@samsung.com>
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Date: Fri, 21 Mar 2025 15:34:42 +0900
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Subject: exfat: fix random stack corruption after get_block
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When get_block is called with a buffer_head allocated on the stack, such
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as do_mpage_readpage, stack corruption due to buffer_head UAF may occur in
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the following race condition situation.
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<CPU 0> <CPU 1>
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mpage_read_folio
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<<bh on stack>>
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do_mpage_readpage
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exfat_get_block
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bh_read
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__bh_read
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get_bh(bh)
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submit_bh
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wait_on_buffer
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...
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end_buffer_read_sync
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__end_buffer_read_notouch
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unlock_buffer
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<<keep going>>
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...
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...
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...
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...
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<<bh is not valid out of mpage_read_folio>>
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.
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.
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another_function
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<<variable A on stack>>
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put_bh(bh)
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atomic_dec(bh->b_count)
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* stack corruption here *
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This patch returns -EAGAIN if a folio does not have buffers when bh_read
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needs to be called. By doing this, the caller can fallback to functions
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like block_read_full_folio(), create a buffer_head in the folio, and then
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call get_block again.
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Let's do not call bh_read() with on-stack buffer_head.
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Fixes: 11a347fb6cef ("exfat: change to get file size from DataLength")
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Cc: stable@vger.kernel.org
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Tested-by: Yeongjin Gil <youngjin.gil@samsung.com>
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Signed-off-by: Sungjong Seo <sj1557.seo@samsung.com>
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Reviewed-by: Yuezhang Mo <Yuezhang.Mo@sony.com>
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Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
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---
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fs/exfat/inode.c | 39 +++++++++++++++++++++++++++++++++------
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1 file changed, 33 insertions(+), 6 deletions(-)
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--- a/fs/exfat/inode.c
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+++ b/fs/exfat/inode.c
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@@ -344,7 +344,8 @@ static int exfat_get_block(struct inode
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* The block has been partially written,
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* zero the unwritten part and map the block.
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*/
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- loff_t size, off, pos;
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+ loff_t size, pos;
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+ void *addr;
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max_blocks = 1;
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@@ -355,17 +356,41 @@ static int exfat_get_block(struct inode
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if (!bh_result->b_folio)
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goto done;
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+ /*
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+ * No buffer_head is allocated.
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+ * (1) bmap: It's enough to fill bh_result without I/O.
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+ * (2) read: The unwritten part should be filled with 0
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+ * If a folio does not have any buffers,
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+ * let's returns -EAGAIN to fallback to
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+ * per-bh IO like block_read_full_folio().
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+ */
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+ if (!folio_buffers(bh_result->b_folio)) {
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+ err = -EAGAIN;
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+ goto done;
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+ }
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+
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pos = EXFAT_BLK_TO_B(iblock, sb);
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size = ei->valid_size - pos;
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- off = pos & (PAGE_SIZE - 1);
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+ addr = folio_address(bh_result->b_folio) +
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+ offset_in_folio(bh_result->b_folio, pos);
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- folio_set_bh(bh_result, bh_result->b_folio, off);
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+ /* Check if bh->b_data points to proper addr in folio */
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+ if (bh_result->b_data != addr) {
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+ exfat_fs_error_ratelimit(sb,
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+ "b_data(%p) != folio_addr(%p)",
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+ bh_result->b_data, addr);
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+ err = -EINVAL;
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+ goto done;
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+ }
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+
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+ /* Read a block */
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err = bh_read(bh_result, 0);
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if (err < 0)
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- goto unlock_ret;
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+ goto done;
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- folio_zero_segment(bh_result->b_folio, off + size,
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- off + sb->s_blocksize);
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+ /* Zero unwritten part of a block */
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+ memset(bh_result->b_data + size, 0,
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+ bh_result->b_size - size);
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} else {
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/*
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* The range has not been written, clear the mapped flag
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@@ -376,6 +401,8 @@ static int exfat_get_block(struct inode
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}
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done:
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bh_result->b_size = EXFAT_BLK_TO_B(max_blocks, sb);
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+ if (err < 0)
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+ clear_buffer_mapped(bh_result);
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unlock_ret:
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mutex_unlock(&sbi->s_lock);
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return err;
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