Patch "hugetlbfs: fix null-ptr-deref in hugetlbfs_parse_param()" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    hugetlbfs: fix null-ptr-deref in hugetlbfs_parse_param()

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     hugetlbfs-fix-null-ptr-deref-in-hugetlbfs_parse_para.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 89977726768d3fe5123997ec97f1120df7fc237a
Author: Hawkins Jiawei <yin31149@xxxxxxxxx>
Date:   Fri Oct 21 07:16:08 2022 +0800

    hugetlbfs: fix null-ptr-deref in hugetlbfs_parse_param()
    
    [ Upstream commit 26215b7ee923b9251f7bb12c4e5f09dc465d35f2 ]
    
    Syzkaller reports a null-ptr-deref bug as follows:
    ======================================================
    KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007]
    RIP: 0010:hugetlbfs_parse_param+0x1dd/0x8e0 fs/hugetlbfs/inode.c:1380
    [...]
    Call Trace:
     <TASK>
     vfs_parse_fs_param fs/fs_context.c:148 [inline]
     vfs_parse_fs_param+0x1f9/0x3c0 fs/fs_context.c:129
     vfs_parse_fs_string+0xdb/0x170 fs/fs_context.c:191
     generic_parse_monolithic+0x16f/0x1f0 fs/fs_context.c:231
     do_new_mount fs/namespace.c:3036 [inline]
     path_mount+0x12de/0x1e20 fs/namespace.c:3370
     do_mount fs/namespace.c:3383 [inline]
     __do_sys_mount fs/namespace.c:3591 [inline]
     __se_sys_mount fs/namespace.c:3568 [inline]
     __x64_sys_mount+0x27f/0x300 fs/namespace.c:3568
     do_syscall_x64 arch/x86/entry/common.c:50 [inline]
     do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
     entry_SYSCALL_64_after_hwframe+0x63/0xcd
     [...]
     </TASK>
    ======================================================
    
    According to commit "vfs: parse: deal with zero length string value",
    kernel will set the param->string to null pointer in vfs_parse_fs_string()
    if fs string has zero length.
    
    Yet the problem is that, hugetlbfs_parse_param() will dereference the
    param->string, without checking whether it is a null pointer.  To be more
    specific, if hugetlbfs_parse_param() parses an illegal mount parameter,
    such as "size=,", kernel will constructs struct fs_parameter with null
    pointer in vfs_parse_fs_string(), then passes this struct fs_parameter to
    hugetlbfs_parse_param(), which triggers the above null-ptr-deref bug.
    
    This patch solves it by adding sanity check on param->string
    in hugetlbfs_parse_param().
    
    Link: https://lkml.kernel.org/r/20221020231609.4810-1-yin31149@xxxxxxxxx
    Reported-by: syzbot+a3e6acd85ded5c16a709@xxxxxxxxxxxxxxxxxxxxxxxxx
    Tested-by: syzbot+a3e6acd85ded5c16a709@xxxxxxxxxxxxxxxxxxxxxxxxx
      Link: https://lore.kernel.org/all/0000000000005ad00405eb7148c6@xxxxxxxxxx/
    Signed-off-by: Hawkins Jiawei <yin31149@xxxxxxxxx>
    Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
    Cc: Hawkins Jiawei <yin31149@xxxxxxxxx>
    Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
    Cc: Ian Kent <raven@xxxxxxxxxx>
    Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 7d039ba5ae28..b1d31c78fc9d 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -1232,7 +1232,7 @@ static int hugetlbfs_parse_param(struct fs_context *fc, struct fs_parameter *par
 
 	case Opt_size:
 		/* memparse() will accept a K/M/G without a digit */
-		if (!isdigit(param->string[0]))
+		if (!param->string || !isdigit(param->string[0]))
 			goto bad_val;
 		ctx->max_size_opt = memparse(param->string, &rest);
 		ctx->max_val_type = SIZE_STD;
@@ -1242,7 +1242,7 @@ static int hugetlbfs_parse_param(struct fs_context *fc, struct fs_parameter *par
 
 	case Opt_nr_inodes:
 		/* memparse() will accept a K/M/G without a digit */
-		if (!isdigit(param->string[0]))
+		if (!param->string || !isdigit(param->string[0]))
 			goto bad_val;
 		ctx->nr_inodes = memparse(param->string, &rest);
 		return 0;
@@ -1258,7 +1258,7 @@ static int hugetlbfs_parse_param(struct fs_context *fc, struct fs_parameter *par
 
 	case Opt_min_size:
 		/* memparse() will accept a K/M/G without a digit */
-		if (!isdigit(param->string[0]))
+		if (!param->string || !isdigit(param->string[0]))
 			goto bad_val;
 		ctx->min_size_opt = memparse(param->string, &rest);
 		ctx->min_val_type = SIZE_STD;