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maccess: Fix writing offset in case of fault in strncpy_from_kernel_nofault()

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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: b58294ead1 ("maccess: allow architectures to provide kernel probing directly")
Signed-off-by: Alban Crequy <albancrequy@linux.microsoft.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Francis Laniel <flaniel@linux.microsoft.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: <stable@vger.kernel.org> [5.8]
Link: https://lore.kernel.org/bpf/20221110085614.111213-2-albancrequy@linux.microsoft.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Alban Crequy 2022-11-10 09:56:13 +01:00 committed by Greg Kroah-Hartman
parent 24cc679abb
commit db744288af
1 changed files with 1 additions and 1 deletions
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2
mm/maccess.c
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@ -83,7 +83,7 @@ long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
return src - unsafe_addr; return src - unsafe_addr;
Efault: Efault:
pagefault_enable(); pagefault_enable();
dst[-1] = '\0'; dst[0] = '\0';
return -EFAULT; return -EFAULT;
} }
#else /* HAVE_GET_KERNEL_NOFAULT */ #else /* HAVE_GET_KERNEL_NOFAULT */