From 9648d760edf4320e23e2b819037501fb44cba291 Mon Sep 17 00:00:00 2001 From: Alban Crequy Date: Thu, 10 Nov 2022 09:56:13 +0100 Subject: [PATCH] maccess: Fix writing offset in case of fault in strncpy_from_kernel_nofault() commit 8678ea06852cd1f819b870c773d43df888d15d46 upstream. 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. Fixes: b58294ead14c ("maccess: allow architectures to provide kernel probing directly") Signed-off-by: Alban Crequy Signed-off-by: Andrii Nakryiko Tested-by: Francis Laniel Reviewed-by: Andrew Morton Cc: [5.8] Link: https://lore.kernel.org/bpf/20221110085614.111213-2-albancrequy@linux.microsoft.com Signed-off-by: Greg Kroah-Hartman --- mm/maccess.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/maccess.c b/mm/maccess.c index d3f1a1f0b1c1..ded4bfaba7f3 100644 --- a/mm/maccess.c +++ b/mm/maccess.c @@ -99,7 +99,7 @@ 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'; return -EFAULT; } #else /* HAVE_GET_KERNEL_NOFAULT */