[RFC PATCH v2 5/6] arm64: signal: Parse extra_context during sigreturn
Dave Martin
Dave.Martin at arm.com
Wed Apr 12 13:01:14 EDT 2017
If extra_context is present, parse it.
To avoid abuse by userspace, this patch attempts to ensure that:
* no more than one extra_context is accepted;
* the extra_context is a sensible size;
* the extra context data is properly aligned.
The extra_context data is required to start immediately after
struct rt_sigframe (as during signal delivery). This serves as a
sanity-check that the signal frame has not been moved or copied
without taking the extra data into account.
Signed-off-by: Dave Martin <Dave.Martin at arm.com>
---
arch/arm64/include/uapi/asm/sigcontext.h | 6 ++++-
arch/arm64/kernel/signal.c | 46 ++++++++++++++++++++++++++++++++
2 files changed, 51 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/include/uapi/asm/sigcontext.h b/arch/arm64/include/uapi/asm/sigcontext.h
index b5e2523..a2f7211 100644
--- a/arch/arm64/include/uapi/asm/sigcontext.h
+++ b/arch/arm64/include/uapi/asm/sigcontext.h
@@ -96,7 +96,11 @@ struct esr_context {
* extra_context must be the last record in sigcontext.__reserved[]
* except for the terminator).
*
- * 4) The extra space must itself be terminated with a null
+ * 4) The extra space to which data points must start at the first
+ * 16-byte aligned address immediately after the end of the sigcontext
+ * strucutre.
+ *
+ * 5) The extra space must itself be terminated with a null
* _aarch64_ctx.
*/
#define EXTRA_MAGIC 0x45585401
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 95547e1..983cddf 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -223,6 +223,10 @@ static int parse_user_sigframe(struct user_ctxs *user,
char __user *base = (char __user *)&sc->__reserved;
size_t offset = 0;
size_t limit = sizeof(sc->__reserved);
+ bool have_extra_context = false;
+
+ /* Expected location of extra_data (if present): */
+ char __user *const extra_base = (char __user *)sf + BASE_SIGFRAME_SIZE;
user->fpsimd = NULL;
@@ -232,6 +236,9 @@ static int parse_user_sigframe(struct user_ctxs *user,
while (1) {
int err = 0;
u32 magic, size;
+ struct extra_context const __user *extra;
+ void __user *extra_data;
+ u32 extra_size;
if (limit - offset < sizeof(*head))
goto invalid;
@@ -269,6 +276,45 @@ static int parse_user_sigframe(struct user_ctxs *user,
/* ignore */
break;
+ case EXTRA_MAGIC:
+ if (have_extra_context)
+ goto invalid;
+
+ if (size < sizeof(*extra))
+ goto invalid;
+
+ extra = (struct extra_context const __user *)head;
+ __get_user_error(extra_data, &extra->data, err);
+ __get_user_error(extra_size, &extra->size, err);
+ if (err)
+ return err;
+
+ /* Prevent looping/repeated parsing of extra_conext */
+ have_extra_context = true;
+
+ /*
+ * Rely on the __user accessors to reject bogus
+ * pointers.
+ */
+ base = extra_data;
+ if (!IS_ALIGNED((unsigned long)base, 16))
+ goto invalid;
+
+ if (extra_data != extra_base)
+ goto invalid;
+
+ /* Reject "unreasonably large" frames: */
+ limit = extra_size;
+ if (limit > SIGFRAME_MAXSZ - sizeof(sc->__reserved))
+ goto invalid;
+
+ /*
+ * Ignore trailing terminator in __reserved[]
+ * and start parsing extra_data:
+ */
+ offset = 0;
+ continue;
+
default:
goto invalid;
}
--
2.1.4
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