Commit 30d1872d authored by Nikolaus Schulz's avatar Nikolaus Schulz Committed by Linus Torvalds
Browse files

fat: fix buffer overflow in vfat_create_shortname() 



When using the string representation of a random counter as part of the base
name, ensure that it is no longer than 4 bytes.

Since we are repeatedly decrementing the counter in a loop until we have found a
unique base name, the counter may wrap around zero; therefore, it is not enough
to mask its higher bits before entering the loop, this must be done inside the
loop.

[hirofumi@mail.parknet.co.jp: use snprintf()]
Signed-off-by: default avatarNikolaus Schulz <microschulz@web.de>
Cc: stable@kernel.org
Signed-off-by: default avatarOGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 2eaa9cfd

fs/fat/namei_vfat.c

+3 −3
Original line number Diff line number Diff line
@@ -309,7 +309,7 @@ static int vfat_create_shortname(struct inode *dir, struct nls_table *nls, 
{

	struct fat_mount_options *opts = &MSDOS_SB(dir->i_sb)->options;

	wchar_t *ip, *ext_start, *end, *name_start;

	unsigned char base[9], ext[4], buf[8], *p;

	unsigned char base[9], ext[4], buf[5], *p;

	unsigned char charbuf[NLS_MAX_CHARSET_SIZE];

	int chl, chi;

	int sz = 0, extlen, baselen, i, numtail_baselen, numtail2_baselen;
@@ -467,7 +467,7 @@ static int vfat_create_shortname(struct inode *dir, struct nls_table *nls, 
			return 0;

	}



	i = jiffies & 0xffff;

	i = jiffies;

	sz = (jiffies >> 16) & 0x7;

	if (baselen > 2) {

		baselen = numtail2_baselen;
@@ -476,7 +476,7 @@ static int vfat_create_shortname(struct inode *dir, struct nls_table *nls, 
	name_res[baselen + 4] = '~';

	name_res[baselen + 5] = '1' + sz;

	while (1) {

		sprintf(buf, "%04X", i);

		snprintf(buf, sizeof(buf), "%04X", i & 0xffff);

		memcpy(&name_res[baselen], buf, 4);

		if (vfat_find_form(dir, name_res) < 0)

			break;

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