From: Gustavo A. R. Silva gustavoars@kernel.org
[ Upstream commit 71e7552c90db2a2767f5c17c7ec72296b0d92061 ]
-Wstringop-overflow is legitimately warning us about extra_size pontentially being zero at some point, hence potenially ending up _allocating_ zero bytes of memory for extra pointer and then trying to access such object in a call to copy_from_user().
Fix this by adding a sanity check to ensure we never end up trying to allocate zero bytes of data for extra pointer, before continue executing the rest of the code in the function.
Address the following -Wstringop-overflow warning seen when built m68k architecture with allyesconfig configuration: from net/wireless/wext-core.c:11: In function '_copy_from_user', inlined from 'copy_from_user' at include/linux/uaccess.h:183:7, inlined from 'ioctl_standard_iw_point' at net/wireless/wext-core.c:825:7: arch/m68k/include/asm/string.h:48:25: warning: '__builtin_memset' writing 1 or more bytes into a region of size 0 overflows the destination [-Wstringop-overflow=] 48 | #define memset(d, c, n) __builtin_memset(d, c, n) | ^~~~~~~~~~~~~~~~~~~~~~~~~ include/linux/uaccess.h:153:17: note: in expansion of macro 'memset' 153 | memset(to + (n - res), 0, res); | ^~~~~~ In function 'kmalloc', inlined from 'kzalloc' at include/linux/slab.h:694:9, inlined from 'ioctl_standard_iw_point' at net/wireless/wext-core.c:819:10: include/linux/slab.h:577:16: note: at offset 1 into destination object of size 0 allocated by '__kmalloc' 577 | return __kmalloc(size, flags); | ^~~~~~~~~~~~~~~~~~~~~~
This help with the ongoing efforts to globally enable -Wstringop-overflow.
Link: https://github.com/KSPP/linux/issues/315 Signed-off-by: Gustavo A. R. Silva gustavoars@kernel.org Reviewed-by: Simon Horman simon.horman@corigine.com Link: https://lore.kernel.org/r/ZItSlzvIpjdjNfd8@work Signed-off-by: Johannes Berg johannes.berg@intel.com Signed-off-by: Sasha Levin sashal@kernel.org --- net/wireless/wext-core.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/net/wireless/wext-core.c b/net/wireless/wext-core.c index b6414c7bef556..4bf33f9b28870 100644 --- a/net/wireless/wext-core.c +++ b/net/wireless/wext-core.c @@ -798,6 +798,12 @@ static int ioctl_standard_iw_point(struct iw_point *iwp, unsigned int cmd, } }
+ /* Sanity-check to ensure we never end up _allocating_ zero + * bytes of data for extra. + */ + if (extra_size <= 0) + return -EFAULT; + /* kzalloc() ensures NULL-termination for essid_compat. */ extra = kzalloc(extra_size, GFP_KERNEL); if (!extra)