From: "Ahmed S. Darwish" 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 Acked-by: Casey Schaufler Signed-off-by: Andrew Morton --- security/smack/smack.h | 8 -------- security/smack/smackfs.c | 31 ++++++++++++++++++++----------- 2 files changed, 20 insertions(+), 19 deletions(-) diff -puN security/smack/smack.h~smackfs-do-not-trust-count-in-inodes-writes security/smack/smack.h --- a/security/smack/smack.h~smackfs-do-not-trust-count-in-inodes-writes +++ a/security/smack/smack.h @@ -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; diff -puN security/smack/smackfs.c~smackfs-do-not-trust-count-in-inodes-writes security/smack/smackfs.c --- a/security/smack/smackfs.c~smackfs-do-not-trust-count-in-inodes-writes +++ a/security/smack/smackfs.c @@ -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_ * 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 fil 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 fi 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 fi 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)); _