On Tue, 8 Nov 2022 12:38:53 -0800 Yonghong Song yhs@meta.com wrote:
On 11/8/22 12:35 PM, Yonghong Song wrote:
On 11/8/22 11:52 AM, Francis Laniel wrote:
From: Alban Crequy albancrequy@microsoft.com
If a page fault occurs while copying the first byte, this function resets one byte before dst. As a consequence, an address could be modified and leaded to kernel crashes if case the modified address was accessed later.
Signed-off-by: Alban Crequy albancrequy@microsoft.com Tested-by: Francis Laniel flaniel@linux.microsoft.com
mm/maccess.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/maccess.c b/mm/maccess.c index 5f4d240f67ec..074f6b086671 100644 --- a/mm/maccess.c +++ b/mm/maccess.c @@ -97,7 +97,7 @@ long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count) return src - unsafe_addr; Efault: pagefault_enable(); - dst[-1] = '\0'; + dst[0] = '\0';
What if the fault is due to dst, so the above won't work, right?
The original code should work fine if the first byte copy is successful. For the first byte copy fault, maybe just to leave it as is?
Okay, the dst is always safe (from func signature), so change looks okay to me. Probably mm people can double check.
My understanding was that the bpf verifier is supposed to check that the dst pointer is safe. But I don't know where it is done, and I don't know how it can check that the dst buffer is big enough.
return -EFAULT; }
-- 2.25.1