[PATCH RESEND] kprobes: be more permissive when user specifies both symbol name and address

[Jianyu Zhan <nasa4836@gmail.com>]

Hi, I found that this patch wasn't merged into mainline during this merge
window(maybe it wasn't cooked in any tree), while it has been acked-by for
a couple of days.

Ingo, would you mind queueing this one? Thanks.

-----<8-----

Currently, if user specifies both symbol name and address, we just
bail out.

This might be too rude. This patch makes it give more tolerance.
If both are specified, check address first, if the symbol found
does not match the one user specify, print a waring. If not found,
return -ENOENT, because some symbols might have muplitple instances,
we don't bother to check symbol name.

Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Jianyu Zhan <nasa4836@gmail.com>
---
 Documentation/kprobes.txt |  4 +++-
 kernel/kprobes.c          | 32 +++++++++++++++++++++++++++++---
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt
index 4bbeca8..49af14e 100644
--- a/Documentation/kprobes.txt
+++ b/Documentation/kprobes.txt
@@ -358,7 +358,9 @@ to install a probepoint is known. This field is used to calculate the
 probepoint.
 
 3. Specify either the kprobe "symbol_name" OR the "addr". If both are
-specified, kprobe registration will fail with -EINVAL.
+specified, only check "addr", because some symbols might have muplitple
+instances. If neither is specified, kprobe registration will fail
+with -EINVAL.
 
 4. With CISC architectures (such as i386 and x86_64), the kprobes code
 does not validate if the kprobe.addr is at an instruction boundary.
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 3214289..81d891b 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1358,15 +1358,41 @@ static bool within_kprobe_blacklist(unsigned long addr)
 static kprobe_opcode_t *kprobe_addr(struct kprobe *p)
 {
 	kprobe_opcode_t *addr = p->addr;
+	char namebuf[KSYM_NAME_LEN];
+	const char *sym_name = NULL;
+	unsigned long offset;
 
-	if ((p->symbol_name && p->addr) ||
-	    (!p->symbol_name && !p->addr))
+	if (!p->symbol_name && !p->addr)
 		goto invalid;
 
-	if (p->symbol_name) {
+	/*
+	 * Some symbols might have muplitple instances,
+	 * so if both specified, only check address.
+	 */
+	if (unlikely(p->addr && p->symbol_name)) {
+		sym_name = kallsyms_lookup((unsigned long)(p->addr),
+				NULL, &offset, NULL, namebuf);
+		if (!sym_name)
+			return ERR_PTR(-ENOENT);
+
+		if (strncmp(sym_name, p->symbol_name, KSYM_NAME_LEN)
+				|| offset != p->offset) {
+			pr_err("Incorrect symbol or offset, should be "
+				"symbol=%s, offset=%ld.\n", sym_name, offset);
+			goto invalid;
+		}
+	} else if (p->symbol_name) {
+		/* Only symbol case */
 		kprobe_lookup_name(p->symbol_name, addr);
 		if (!addr)
 			return ERR_PTR(-ENOENT);
+	} else {
+		/*
+		 * Only address case.
+		 * Since we later will do sanity check of the
+		 * address range in check_kprobe_address_safe(),
+		 * do nothing here.
+		 */
 	}
 
 	addr = (kprobe_opcode_t *)(((char *)addr) + p->offset);
-- 
2.0.0