[PATCH 2/3] vfs: Fix implicit conversion problem when testing overflow case

[Julian Sun <sunjunchao2870@gmail.com>]

The overflow check in generic_copy_file_checks() and generic_remap_checks()
is now broken because the result of the addition is implicitly converted to
an unsigned type, which disrupts the comparison with signed numbers.
This caused the kernel to not return EOVERFLOW in copy_file_range()
call with len is set to 0xffffffffa003e45bul.

Use the check_add_overflow() macro to fix this issue.

Reported-and-tested-by: syzbot+296b1c84b9cbf306e5a0@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=296b1c84b9cbf306e5a0
Fixes: 1383a7ed6749 ("vfs: check file ranges before cloning files")
Fixes: 96e6e8f4a68d ("vfs: add missing checks to copy_file_range")
Inspired-by: Dave Chinner <david@fromorbit.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Julian Sun <sunjunchao2870@gmail.com>
---
 fs/read_write.c  | 5 +++--
 fs/remap_range.c | 5 +++--
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index 070a7c33b9dd..5211246edc2e 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1509,7 +1509,7 @@ static int generic_copy_file_checks(struct file *file_in, loff_t pos_in,
 	struct inode *inode_in = file_inode(file_in);
 	struct inode *inode_out = file_inode(file_out);
 	uint64_t count = *req_count;
-	loff_t size_in;
+	loff_t size_in, tmp;
 	int ret;
 
 	ret = generic_file_rw_checks(file_in, file_out);
@@ -1544,7 +1544,8 @@ static int generic_copy_file_checks(struct file *file_in, loff_t pos_in,
 		return -ETXTBSY;
 
 	/* Ensure offsets don't wrap. */
-	if (pos_in + count < pos_in || pos_out + count < pos_out)
+	if (check_add_overflow(pos_in, count, &tmp) ||
+	    check_add_overflow(pos_out, count, &tmp))
 		return -EOVERFLOW;
 
 	/* Shorten the copy to EOF */
diff --git a/fs/remap_range.c b/fs/remap_range.c
index 28246dfc8485..6fdeb3c8cb70 100644
--- a/fs/remap_range.c
+++ b/fs/remap_range.c
@@ -36,7 +36,7 @@ static int generic_remap_checks(struct file *file_in, loff_t pos_in,
 	struct inode *inode_out = file_out->f_mapping->host;
 	uint64_t count = *req_count;
 	uint64_t bcount;
-	loff_t size_in, size_out;
+	loff_t size_in, size_out, tmp;
 	loff_t bs = inode_out->i_sb->s_blocksize;
 	int ret;
 
@@ -45,7 +45,8 @@ static int generic_remap_checks(struct file *file_in, loff_t pos_in,
 		return -EINVAL;
 
 	/* Ensure offsets don't wrap. */
-	if (pos_in + count < pos_in || pos_out + count < pos_out)
+	if (check_add_overflow(pos_in, count, &tmp) ||
+	    check_add_overflow(pos_out, count, &tmp))
 		return -EINVAL;
 
 	size_in = i_size_read(inode_in);
-- 
2.39.2