diff mbox series

[bpf,v2,1/2] maccess: fix writing offset in case of fault in strncpy_from_kernel_nofault()

Message ID 20221110085614.111213-2-albancrequy@linux.microsoft.com (mailing list archive)
State New
Headers show
Series Fix offset when fault occurs in strncpy_from_kernel_nofault() | expand

Commit Message

Alban Crequy Nov. 10, 2022, 8:56 a.m. UTC 
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")
Cc: <stable@vger.kernel.org> [5.8]
Signed-off-by: Alban Crequy <albancrequy@linux.microsoft.com>
Tested-by: Francis Laniel <flaniel@linux.microsoft.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>

---

Changes v1 to v2:
- add 'cc:stable', 'Fixes:' and review tag
- fix my email
- rebase on bpf tree and tag for bpf tree
---
 mm/maccess.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff mbox series

Patch

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';
 	return -EFAULT;
 }