| Message ID | 20120718210825.GA3145@fieldses.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 07/18/2012 11:33 PM, Sasha Levin wrote: > On 07/18/2012 11:08 PM, J. Bruce Fields wrote: >> On Wed, Jul 18, 2012 at 04:00:49PM -0400, Jim Rees wrote: >>> J. Bruce Fields wrote: >>> >>> On Tue, Jul 17, 2012 at 12:01:26AM +0200, Sasha Levin wrote: >>> > The buffer size in read_flush() is too small for the longest possible values >>> > for it. This can lead to a kernel stack corruption: >>> >>> Thanks! >>> >>> > >>> > diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c >>> > index 2afd2a8..f86d95e 100644 >>> > --- a/net/sunrpc/cache.c >>> > +++ b/net/sunrpc/cache.c >>> > @@ -1409,11 +1409,11 @@ static ssize_t read_flush(struct file *file, char __user *buf, >>> > size_t count, loff_t *ppos, >>> > struct cache_detail *cd) >>> > { >>> > - char tbuf[20]; >>> > + char tbuf[22]; >>> >>> I wonder how common this sort of calculation is in the kernel? It might >>> provide some peace of mind to be able to write this something like >>> >>> char tbuf[MAXLEN_BASE10_UL + 2] /* + 2 for final "\n\0" */ >>> >>> You could use something like: >>> >>> char tbuf[sizeof (unsigned long) * 24 / 10 + 1 + 2]; /* + 2 for final "\n\0" */ >>> >>> since there are roughly 10 bits for every 3 decimal digits. >> >> So we could do something like this. OK, I'm not sure I care enough. >> >> --b. >> >> diff --git a/include/linux/string.h b/include/linux/string.h >> index e033564..ed34180 100644 >> --- a/include/linux/string.h >> +++ b/include/linux/string.h >> @@ -126,6 +126,10 @@ extern void argv_free(char **argv); >> extern bool sysfs_streq(const char *s1, const char *s2); >> extern int strtobool(const char *s, bool *res); >> >> +/* length of the decimal representation of an unsigned integer. Just an >> + * approximation, but it's right for types of size 1 to 36 bytes: */ >> +#define base10len(i) (sizeof(i) * 24 / 10 + 1) >> + >> #ifdef CONFIG_BINARY_PRINTF >> int vbin_printf(u32 *bin_buf, size_t size, const char *fmt, va_list args); >> int bstr_printf(char *buf, size_t size, const char *fmt, const u32 *bin_buf); >> diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c >> index 2afd2a8..1dcd2b3 100644 >> --- a/net/sunrpc/cache.c >> +++ b/net/sunrpc/cache.c >> @@ -1409,7 +1409,7 @@ static ssize_t read_flush(struct file *file, char __user *buf, >> size_t count, loff_t *ppos, >> struct cache_detail *cd) >> { >> - char tbuf[20]; >> + char tbuf[base10len(unsigned long) + 2]; >> unsigned long p = *ppos; >> size_t len; >> >> > > Learning from what happened in this specific case, there are actually 2 issues here: > > - Array size was constant and too small, which is solved by the patch above. > - We were blindly trying to sprintf() into that array, this issue may pop back up if someone decides to change the format string forgetting to modify the array declaration. > > What about adding the following itoa() type helper: Fat fingers :( Something like this (which obviously needs tons of work): #define base10len(i) (sizeof(i) * 24 / 10 + 1) #define itoa(x) \ ({ \ static char str[base10len(x)]; \ sprintf(str, "%lu", (x)); \ str; \ }) -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Sasha Levin wrote: > Learning from what happened in this specific case, there are actually 2 issues here: > > - Array size was constant and too small, which is solved by the patch above. > - We were blindly trying to sprintf() into that array, this issue may pop back up if someone decides to change the format string forgetting to modify the array declaration. > The original patch changed the sprintf to snprintf, and that still seems like a good idea. -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/linux/string.h b/include/linux/string.h index e033564..ed34180 100644 --- a/include/linux/string.h +++ b/include/linux/string.h @@ -126,6 +126,10 @@ extern void argv_free(char **argv); extern bool sysfs_streq(const char *s1, const char *s2); extern int strtobool(const char *s, bool *res); +/* length of the decimal representation of an unsigned integer. Just an + * approximation, but it's right for types of size 1 to 36 bytes: */ +#define base10len(i) (sizeof(i) * 24 / 10 + 1) + #ifdef CONFIG_BINARY_PRINTF int vbin_printf(u32 *bin_buf, size_t size, const char *fmt, va_list args); int bstr_printf(char *buf, size_t size, const char *fmt, const u32 *bin_buf); diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c index 2afd2a8..1dcd2b3 100644 --- a/net/sunrpc/cache.c +++ b/net/sunrpc/cache.c @@ -1409,7 +1409,7 @@ static ssize_t read_flush(struct file *file, char __user *buf, size_t count, loff_t *ppos, struct cache_detail *cd) { - char tbuf[20]; + char tbuf[base10len(unsigned long) + 2]; unsigned long p = *ppos; size_t len;