[PATCH] symbols: handle module symbols outside strbuf

[Stephen Brennan <stephen.s.brennan@oracle.com>]

Module symbol names can get overwritten by live patches or ksplice in
odd corner cases, so that the pointer no longer points within the string
buffer. Gracefully fallback to reading the string directly from the
kernel image in these cases, to avoid possible segmentation faults
reading outside the bounds of strbuf.

Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
---

Hi folks - I encountered a segfault on a vmcore which had a module
symbol that had gotten its name overwritten by a ksplice (live patch).
It seems like there's not a guarantee that module symbol names _must_
live within the same symbol buffer, and there is even logic to prevent
reading too much data into strbuf in those cases.

This patch simply ensures that symbol names which start outside of the
strbuf which we copied, are read directly from the kernel image, rather
than indexing past the bounds of strbuf. I encountered this in
store_module_symbols_v2() and have tested it there, but I replicated the
code to the other versions. I will try to test it out on the other
variants as well, but I thought I'd share the patch now.

 symbols.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/symbols.c b/symbols.c
index 176c950..e70dd69 100644
--- a/symbols.c
+++ b/symbols.c
@@ -1704,7 +1704,7 @@ store_module_symbols_v1(ulong total, int mods_installed)
 
 			BZERO(buf1, BUFSIZE);
 
-			if (strbuf) 
+			if (strbuf && (unsigned long)modsym->name - first < strbuflen)
 				strcpy(buf1,
 					&strbuf[(ulong)modsym->name - first]);
 			else 
@@ -2080,7 +2080,7 @@ store_module_symbols_6_4(ulong total, int mods_installed)
 
 			BZERO(buf1, BUFSIZE);
 
-			if (strbuf)
+			if (strbuf && modsym_name(syms, modsym, i) - first < strbuflen)
 				strcpy(buf1, &strbuf[modsym_name(syms, modsym, i) - first]);
 			else
 				read_string(modsym_name(syms, modsym, i), buf1, BUFSIZE-1);
@@ -2148,7 +2148,7 @@ store_module_symbols_6_4(ulong total, int mods_installed)
 
 			BZERO(buf1, BUFSIZE);
 
-			if (strbuf)
+			if (strbuf && modsym_name(gpl_syms, modsym, i) - first < strbuflen)
 				strcpy(buf1, &strbuf[modsym_name(gpl_syms, modsym, i) - first]);
 			else
 				read_string(modsym_name(gpl_syms, modsym, i), buf1, BUFSIZE-1);
@@ -2456,7 +2456,7 @@ store_module_symbols_v2(ulong total, int mods_installed)
 
 			BZERO(buf1, BUFSIZE);
 
-			if (strbuf) 
+			if (strbuf && modsym_name(syms, modsym, i) - first < strbuflen)
 				strcpy(buf1,
 					&strbuf[modsym_name(syms, modsym, i) - first]);
 			else 
@@ -2529,7 +2529,7 @@ store_module_symbols_v2(ulong total, int mods_installed)
 
 			BZERO(buf1, BUFSIZE);
 
-			if (strbuf) 
+			if (strbuf && modsym_name(gpl_syms, modsym, i) - first < strbuflen)
 				strcpy(buf1,
 					&strbuf[modsym_name(gpl_syms, modsym, i) - first]);
 			else 
-- 
2.39.3