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smackfs: do not trust `count' in inodes write()s

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Smackfs write() implementation does not put a higher bound on the number of
bytes to copy from user-space.  This may lead to a DOS attack if a malicious
`count' field is given.

Assure that given `count' is exactly the length needed for a /smack/load rule.
 In case of /smack/cipso where the length is relative, assure that `count'
does not exceed the size needed for a buffer representing maximum possible
number of CIPSO 2.2 categories.

Signed-off-by: Ahmed S. Darwish <darwish.07@gmail.com>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Ahmed S. Darwish 2008-03-13 12:32:34 -07:00 committed by Linus Torvalds
parent 93d74463d0
commit b500ce8d24
2 changed files with 20 additions and 19 deletions
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8
security/smack/smack.h
View file

@ -26,14 +26,6 @@
#define SMK_MAXLEN 23
#define SMK_LABELLEN (SMK_MAXLEN+1)
/*
* How many kinds of access are there?
* Here's your answer.
*/
#define SMK_ACCESSDASH '-'
#define SMK_ACCESSLOW "rwxa"
#define SMK_ACCESSKINDS (sizeof(SMK_ACCESSLOW) - 1)
struct superblock_smack {
char *smk_root;
char *smk_floor;

31
security/smack/smackfs.c
View file

@ -81,10 +81,23 @@ static struct semaphore smack_write_sem;
/*
* Values for parsing cipso rules
* SMK_DIGITLEN: Length of a digit field in a rule.
* SMK_CIPSOMEN: Minimum possible cipso rule length.
* SMK_CIPSOMIN: Minimum possible cipso rule length.
* SMK_CIPSOMAX: Maximum possible cipso rule length.
*/
#define SMK_DIGITLEN 4
#define SMK_CIPSOMIN (SMK_MAXLEN + 2 * SMK_DIGITLEN)
#define SMK_CIPSOMIN (SMK_LABELLEN + 2 * SMK_DIGITLEN)
#define SMK_CIPSOMAX (SMK_CIPSOMIN + SMACK_CIPSO_MAXCATNUM * SMK_DIGITLEN)
/*
* Values for parsing MAC rules
* SMK_ACCESS: Maximum possible combination of access permissions
* SMK_ACCESSLEN: Maximum length for a rule access field
* SMK_LOADLEN: Smack rule length
*/
#define SMK_ACCESS "rwxa"
#define SMK_ACCESSLEN (sizeof(SMK_ACCESS) - 1)
#define SMK_LOADLEN (SMK_LABELLEN + SMK_LABELLEN + SMK_ACCESSLEN)
/*
* Seq_file read operations for /smack/load
@ -229,14 +242,10 @@ static void smk_set_access(struct smack_rule *srp)
* The format is exactly:
* char subject[SMK_LABELLEN]
* char object[SMK_LABELLEN]
* char access[SMK_ACCESSKINDS]
* char access[SMK_ACCESSLEN]
*
* Anything following is commentary and ignored.
*
* writes must be SMK_LABELLEN+SMK_LABELLEN+4 bytes.
* writes must be SMK_LABELLEN+SMK_LABELLEN+SMK_ACCESSLEN bytes.
*/
#define MINIMUM_LOAD (SMK_LABELLEN + SMK_LABELLEN + SMK_ACCESSKINDS)
static ssize_t smk_write_load(struct file *file, const char __user *buf,
size_t count, loff_t *ppos)
{
@ -253,7 +262,7 @@ static ssize_t smk_write_load(struct file *file, const char __user *buf,
return -EPERM;
if (*ppos != 0)
return -EINVAL;
if (count < MINIMUM_LOAD)
if (count != SMK_LOADLEN)
return -EINVAL;
data = kzalloc(count, GFP_KERNEL);
@ -513,7 +522,7 @@ static ssize_t smk_write_cipso(struct file *file, const char __user *buf,
return -EPERM;
if (*ppos != 0)
return -EINVAL;
if (count <= SMK_CIPSOMIN)
if (count < SMK_CIPSOMIN || count > SMK_CIPSOMAX)
return -EINVAL;
data = kzalloc(count + 1, GFP_KERNEL);
@ -547,7 +556,7 @@ static ssize_t smk_write_cipso(struct file *file, const char __user *buf,
if (ret != 1 || catlen > SMACK_CIPSO_MAXCATNUM)
goto out;
if (count <= (SMK_CIPSOMIN + catlen * SMK_DIGITLEN))
if (count != (SMK_CIPSOMIN + catlen * SMK_DIGITLEN))
goto out;
memset(mapcatset, 0, sizeof(mapcatset));