Re: [f2fs-dev] [PATCH] f2fs: fix to do sanity check with inode.i_inline_xattr_size

[Sahitya Tummala]

On Fri, Mar 01, 2019 at 03:38:05PM +0800, Chao Yu wrote:
> As Paul Bandha reported in bugzilla:
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=202709
> 
> When I run the poc on the mounted f2fs img I get a buffer overflow in
> read_inline_xattr due to there being no sanity check on the value of
> i_inline_xattr_size.
> 
> I created the img by just modifying the value of i_inline_xattr_size
> in the inode:
> 
> i_name                        		[test1.txt]
> i_ext: fofs:0 blkaddr:0 len:0
> i_extra_isize                 		[0x      18 : 24]
> i_inline_xattr_size           		[0x    ffff : 65535]
> i_addr[ofs]                   		[0x       0 : 0]
> 
> mkdir /mnt/f2fs
> mount ./f2fs1.img /mnt/f2fs
> gcc poc.c -o poc
> ./poc
> 
> int main() {
> 	int y = syscall(SYS_listxattr, "/mnt/f2fs/test1.txt", NULL, 0);
> 	printf("ret %d", y);
> 	printf("errno: %d\n", errno);
> 
> }
> 
>  BUG: KASAN: slab-out-of-bounds in read_inline_xattr+0x18f/0x260
>  Read of size 262140 at addr ffff88011035efd8 by task f2fs1poc/3263
> 
>  CPU: 0 PID: 3263 Comm: f2fs1poc Not tainted 4.18.0-custom #1
>  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.11.1-0-g0551a4be2c-prebuilt.qemu-project.org 04/01/2014
>  Call Trace:
>   dump_stack+0x71/0xab
>   print_address_description+0x83/0x250
>   kasan_report+0x213/0x350
>   memcpy+0x1f/0x50
>   read_inline_xattr+0x18f/0x260
>   read_all_xattrs+0xba/0x190
>   f2fs_listxattr+0x9d/0x3f0
>   listxattr+0xb2/0xd0
>   path_listxattr+0x93/0xe0
>   do_syscall_64+0x9d/0x220
>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Let's add sanity check for inode.i_inline_xattr_size during f2fs_iget()
> to avoid this issue.
> 
> Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
> ---
>  fs/f2fs/inode.c | 14 ++++++++++++++
>  fs/f2fs/super.c |  7 ++-----
>  fs/f2fs/xattr.h |  9 +++++++++
>  3 files changed, 25 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
> index bec52961630b..b132fe2ff779 100644
> --- a/fs/f2fs/inode.c
> +++ b/fs/f2fs/inode.c
> @@ -14,6 +14,7 @@
>  #include "f2fs.h"
>  #include "node.h"
>  #include "segment.h"
> +#include "xattr.h"
>  
>  #include <trace/events/f2fs.h>
>  
> @@ -248,6 +249,19 @@ static bool sanity_check_inode(struct inode *inode, struct page *node_page)
>  		return false;
>  	}
>  
> +	if (f2fs_has_extra_attr(inode) &&
> +		f2fs_sb_has_flexible_inline_xattr(sbi) &&
> +		(fi->i_inline_xattr_size < MIN_INLINE_XATTR_SIZE ||
> +		fi->i_inline_xattr_size > MAX_INLINE_XATTR_SIZE)) {
> +		set_sbi_flag(sbi, SBI_NEED_FSCK);
> +		f2fs_msg(sbi->sb, KERN_WARNING,
> +			"%s: inode (ino=%lx) has corrupted "
> +			"i_inline_xattr_size: %d, min: %zu, max: %zu",
> +			__func__, inode->i_ino, fi->i_inline_xattr_size,
> +			MIN_INLINE_XATTR_SIZE, MAX_INLINE_XATTR_SIZE);
> +		return false;
> +	}
> +
>  	if (F2FS_I(inode)->extent_tree) {
>  		struct extent_info *ei = &F2FS_I(inode)->extent_tree->largest;
>  
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index 42eb5c86330a..9184b7524c03 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -835,12 +835,9 @@ static int parse_options(struct super_block *sb, char *options)
>  			return -EINVAL;
>  		}
>  		if (F2FS_OPTION(sbi).inline_xattr_size <
> -			sizeof(struct f2fs_xattr_header) / sizeof(__le32) ||
> +			MIN_INLINE_XATTR_SIZE ||
>  			F2FS_OPTION(sbi).inline_xattr_size >
> -			DEF_ADDRS_PER_INODE -
> -			F2FS_TOTAL_EXTRA_ATTR_SIZE / sizeof(__le32) -
> -			DEF_INLINE_RESERVED_SIZE -
> -			MIN_INLINE_DENTRY_SIZE / sizeof(__le32)) {
> +			MAX_INLINE_XATTR_SIZE) {
>  			f2fs_msg(sb, KERN_ERR,
>  					"inline xattr size is out of range");
>  			return -EINVAL;
> diff --git a/fs/f2fs/xattr.h b/fs/f2fs/xattr.h
> index 67db134da0f5..94e8a5eeaae1 100644
> --- a/fs/f2fs/xattr.h
> +++ b/fs/f2fs/xattr.h
> @@ -55,6 +55,8 @@ struct f2fs_xattr_entry {
>  #define XATTR_FIRST_ENTRY(ptr)	(XATTR_ENTRY(XATTR_HDR(ptr) + 1))
>  #define XATTR_ROUND		(3)
>  
> +#define XATTR_HDR_SIZE		(sizeof(struct f2fs_xattr_header))
> +
>  #define XATTR_ALIGN(size)	(((size) + XATTR_ROUND) & ~XATTR_ROUND)
>  
>  #define ENTRY_SIZE(entry) (XATTR_ALIGN(sizeof(struct f2fs_xattr_entry) + \
> @@ -78,6 +80,13 @@ struct f2fs_xattr_entry {
>  				sizeof(struct f2fs_xattr_header) -	\
>  				sizeof(struct f2fs_xattr_entry))
>  
> +#define MAX_INLINE_XATTR_SIZE	(XATTR_HDR_SIZE / sizeof(__le32))

I think this should be MIN_INLINE_XATTR_SIZE.

> +#define MIN_INLINE_XATTR_SIZE						\
> +			(DEF_ADDRS_PER_INODE -				\
> +			F2FS_TOTAL_EXTRA_ATTR_SIZE / sizeof(__le32) -	\
> +			DEF_INLINE_RESERVED_SIZE -			\
> +			MIN_INLINE_DENTRY_SIZE / sizeof(__le32))
> +

And this should be MAX_INLINE_XATTR_SIZE.

Thanks,
Sahitya.

>  /*
>   * On-disk structure of f2fs_xattr
>   * We use inline xattrs space + 1 block for xattr.
> -- 
> 2.18.0.rc1
> 
> 
> 
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