Commit b32a09db authored by Markus Armbruster's avatar Markus Armbruster Committed by Eric Van Hensbergen
Browse files

add match_strlcpy() us it to make v9fs make uname and remotename parsing more robust 



match_strcpy() is a somewhat creepy function: the caller needs to make sure
that the destination buffer is big enough, and when he screws up or
forgets, match_strcpy() happily overruns the buffer.

There's exactly one customer: v9fs_parse_options().  I believe it currently
can't overflow its buffer, but that's not exactly obvious.

The source string is a substing of the mount options.  The kernel silently
truncates those to PAGE_SIZE bytes, including the terminating zero.  See
compat_sys_mount() and do_mount().

The destination buffer is obtained from __getname(), which allocates from
name_cachep, which is initialized by vfs_caches_init() for size PATH_MAX.

We're safe as long as PATH_MAX <= PAGE_SIZE.  PATH_MAX is 4096.  As far as
I know, the smallest PAGE_SIZE is also 4096.

Here's a patch that makes the code a bit more obviously correct.  It
doesn't depend on PATH_MAX <= PAGE_SIZE.

Signed-off-by: default avatarMarkus Armbruster <armbru@redhat.com>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Cc: Jim Meyering <meyering@redhat.com>
Cc: "Randy.Dunlap" <rdunlap@xenotime.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarEric Van Hensbergen <ericvh@gmail.com>
parent dd286422

fs/9p/v9fs.c

+2 −2
Original line number Diff line number Diff line
@@ -125,10 +125,10 @@ static void v9fs_parse_options(struct v9fs_session_info *v9ses) 
			v9ses->afid = option;

			break;

		case Opt_uname:

			match_strcpy(v9ses->uname, &args[0]);

			match_strlcpy(v9ses->uname, &args[0], PATH_MAX);

			break;

		case Opt_remotename:

			match_strcpy(v9ses->aname, &args[0]);

			match_strlcpy(v9ses->aname, &args[0], PATH_MAX);

			break;

		case Opt_nodevmap:

			v9ses->nodev = 1;

include/linux/parser.h

+1 −1
Original line number Diff line number Diff line
@@ -29,5 +29,5 @@ int match_token(char *, match_table_t table, substring_t args[]); 
int match_int(substring_t *, int *result);

int match_octal(substring_t *, int *result);

int match_hex(substring_t *, int *result);

void match_strcpy(char *, const substring_t *);

size_t match_strlcpy(char *, const substring_t *, size_t);

char *match_strdup(const substring_t *);

lib/parser.c

+20 −12
Original line number Diff line number Diff line
@@ -182,18 +182,25 @@ int match_hex(substring_t *s, int *result) 
}



/**

 * match_strcpy: - copies the characters from a substring_t to a string

 * @to: string to copy characters to.

 * @s: &substring_t to copy

 * match_strlcpy: - Copy the characters from a substring_t to a sized buffer

 * @dest: where to copy to

 * @src: &substring_t to copy

 * @size: size of destination buffer

 *

 * Description: Copies the set of characters represented by the given

 * &substring_t @s to the c-style string @to. Caller guarantees that @to is

 * large enough to hold the characters of @s.

 * Description: Copy the characters in &substring_t @src to the

 * c-style string @dest.  Copy no more than @size - 1 characters, plus

 * the terminating NUL.  Return length of @src.

 */

void match_strcpy(char *to, const substring_t *s)

size_t match_strlcpy(char *dest, const substring_t *src, size_t size)

{

	memcpy(to, s->from, s->to - s->from);

	to[s->to - s->from] = '\0';

	size_t ret = src->to - src->from;



	if (size) {

		size_t len = ret >= size ? size - 1 : ret;

		memcpy(dest, src->from, len);

		dest[len] = '\0';

	}

	return ret;

}



/**
@@ -206,9 +213,10 @@ void match_strcpy(char *to, const substring_t *s) 
 */

char *match_strdup(const substring_t *s)

{

	char *p = kmalloc(s->to - s->from + 1, GFP_KERNEL);

	size_t sz = s->to - s->from + 1;

	char *p = kmalloc(sz, GFP_KERNEL);

	if (p)

		match_strcpy(p, s);

		match_strlcpy(p, s, sz);

	return p;

}
@@ -216,5 +224,5 @@ EXPORT_SYMBOL(match_token); 
EXPORT_SYMBOL(match_int);

EXPORT_SYMBOL(match_octal);

EXPORT_SYMBOL(match_hex);

EXPORT_SYMBOL(match_strcpy);

EXPORT_SYMBOL(match_strlcpy);

EXPORT_SYMBOL(match_strdup);

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