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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Daniel Axtens <dja@axtens.net>
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Date: Mon, 20 Dec 2021 21:55:43 +1100
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Subject: [PATCH] net/dns: Don't read past the end of the string we're checking
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against
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I don't really understand what's going on here but fuzzing found
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a bug where we read past the end of check_with. That's a C string,
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so use grub_strlen() to make sure we don't overread it.
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Signed-off-by: Daniel Axtens <dja@axtens.net>
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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(cherry picked from commit 6a97b3f4b1d5173aa516edc6dedbc63de7306d21)
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---
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grub-core/net/dns.c | 19 ++++++++++++++++---
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1 file changed, 16 insertions(+), 3 deletions(-)
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diff --git a/grub-core/net/dns.c b/grub-core/net/dns.c
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index 135faac035..17961a9f18 100644
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--- a/grub-core/net/dns.c
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+++ b/grub-core/net/dns.c
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@@ -146,11 +146,18 @@ check_name_real (const grub_uint8_t *name_at, const grub_uint8_t *head,
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int *length, char *set)
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{
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const char *readable_ptr = check_with;
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+ int readable_len;
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const grub_uint8_t *ptr;
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char *optr = set;
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int bytes_processed = 0;
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if (length)
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*length = 0;
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+
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+ if (readable_ptr != NULL)
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+ readable_len = grub_strlen (readable_ptr);
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+ else
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+ readable_len = 0;
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+
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for (ptr = name_at; ptr < tail && bytes_processed < tail - head + 2; )
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{
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/* End marker. */
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@@ -172,13 +179,16 @@ check_name_real (const grub_uint8_t *name_at, const grub_uint8_t *head,
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ptr = head + (((ptr[0] & 0x3f) << 8) | ptr[1]);
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continue;
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}
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- if (readable_ptr && grub_memcmp (ptr + 1, readable_ptr, *ptr) != 0)
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+ if (readable_ptr != NULL && (*ptr > readable_len || grub_memcmp (ptr + 1, readable_ptr, *ptr) != 0))
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return 0;
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if (grub_memchr (ptr + 1, 0, *ptr)
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|| grub_memchr (ptr + 1, '.', *ptr))
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return 0;
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if (readable_ptr)
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- readable_ptr += *ptr;
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+ {
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+ readable_ptr += *ptr;
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+ readable_len -= *ptr;
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+ }
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if (readable_ptr && *readable_ptr != '.' && *readable_ptr != 0)
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return 0;
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bytes_processed += *ptr + 1;
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@@ -192,7 +202,10 @@ check_name_real (const grub_uint8_t *name_at, const grub_uint8_t *head,
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if (optr)
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*optr++ = '.';
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if (readable_ptr && *readable_ptr)
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- readable_ptr++;
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+ {
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+ readable_ptr++;
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+ readable_len--;
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+ }
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ptr += *ptr + 1;
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}
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return 0;
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