perf tool: Fix use after free in filename__read_build_id

PATCH In review Mitchell Krome 4 participants 4 messages Dec 16, 2014 – Dec 18, 2014 perf events

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Mitchell Krome

author

2014-12-16 02:16 UTC #0 lore raw

PATCH 1/1 perf tool: Fix use after free in filename__read_build_id

In filename__read_build_id, phdr points to memory in buf, which gets realloced before a call to fseek that uses phdr->p_offset. This change stores the value of p_offset before buf is realloced, so the fseek can use the value safely.

Signed-off-by Mitchell Krome <[email protected]>

---
 tools/perf/util/symbol-minimal.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

tools/perf/util/symbol-minimal.c +6 -2

index fa585c6..d7efb03 100644
@@ -129,6 +129,7 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
 
 		for (i = 0, phdr = buf; i < ehdr.e_phnum; i++, phdr++) {
 			void *tmp;
+			long offset;
 
 			if (need_swap) {
 				phdr->p_type = bswap_32(phdr->p_type);

@@ -140,12 +141,13 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
 				continue;
 
 			buf_size = phdr->p_filesz;
+			offset = phdr->p_offset;
 			tmp = realloc(buf, buf_size);
 			if (tmp == NULL)
 				goto out_free;
 
 			buf = tmp;
-			fseek(fp, phdr->p_offset, SEEK_SET);
+			fseek(fp, offset, SEEK_SET);
 			if (fread(buf, buf_size, 1, fp) != 1)
 				goto out_free;

@@ -178,6 +180,7 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
 
 		for (i = 0, phdr = buf; i < ehdr.e_phnum; i++, phdr++) {
 			void *tmp;
+			long offset;
 
 			if (need_swap) {
 				phdr->p_type = bswap_32(phdr->p_type);

@@ -189,12 +192,13 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
 				continue;
 
 			buf_size = phdr->p_filesz;
+			offset = phdr->p_offset;
 			tmp = realloc(buf, buf_size);
 			if (tmp == NULL)
 				goto out_free;
 
 			buf = tmp;
-			fseek(fp, phdr->p_offset, SEEK_SET);
+			fseek(fp, offset, SEEK_SET);
 			if (fread(buf, buf_size, 1, fp) != 1)
 				goto out_free;

Signature · 1 line

1.9.1

Jiri Olsa

Acked-by on v1 1/1

2014-12-16 15:35 UTC #1 lore raw

Quoted 23 lines · Mitchell Krome

In filename__read_build_id, phdr points to memory in buf, which gets realloced before a call to fseek that uses phdr->p_offset. This change stores the value of p_offset before buf is realloced, so the fseek can use the value safely.
Signed-off-by Mitchell Krome <[email protected]>
---
 tools/perf/util/symbol-minimal.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
tools/perf/util/symbol-minimal.c +1 -0
index fa585c6..d7efb03 100644
@@ -129,6 +129,7 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
 
 		for (i = 0, phdr = buf; i < ehdr.e_phnum; i++, phdr++) {
 			void *tmp;
+			long offset;
 
 			if (need_swap) {
 				phdr->p_type = bswap_32(phdr->p_type);
@@ -140,12 +141,13 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
 				continue;

tools/perf/util/symbol-minimal.c int filename__read_build_id(const char *filename, void *bf, size_t size) · line 150

Quoted 10 lines

tools/perf/util/symbol-minimal.c +2 -1

 
 			buf_size = phdr->p_filesz;
+			offset = phdr->p_offset;
 			tmp = realloc(buf, buf_size);
 			if (tmp == NULL)
 				goto out_free;
 
 			buf = tmp;
-			fseek(fp, phdr->p_offset, SEEK_SET);
+			fseek(fp, offset, SEEK_SET);

so the concern is that the realloc buf_size will be smaller than the 'buf' offset of phdr->p_offset value, right? Anyway:

Acked-by Jiri Olsa <[email protected]>

jirka

Arnaldo Carvalho de Melo

maintainer

2014-12-16 16:35 UTC #2 lore raw

Em Tue, Dec 16, 2014 at 04:35:23PM +0100, Jiri Olsa escreveu:

Quoted 31 lines · Mitchell Krome

Quoted 30 lines

Signed-off-by Mitchell Krome <[email protected]>

---
 tools/perf/util/symbol-minimal.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

tools/perf/util/symbol-minimal.c +2 -0

index fa585c6..d7efb03 100644
@@ -129,6 +129,7 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
 
 		for (i = 0, phdr = buf; i < ehdr.e_phnum; i++, phdr++) {
 			void *tmp;
+			long offset;
 
 			if (need_swap) {
 				phdr->p_type = bswap_32(phdr->p_type);

@@ -140,12 +141,13 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
 				continue;
 
 			buf_size = phdr->p_filesz;
+			offset = phdr->p_offset;
 			tmp = realloc(buf, buf_size);
 			if (tmp == NULL)
 				goto out_free;

Quoted 6 lines

tools/perf/util/symbol-minimal.c int filename__read_build_id(const char *filename, void *bf, size_t size) · line 150
Quoted 3 lines
tools/perf/util/symbol-minimal.c +1 -1
 			buf = tmp;
-			fseek(fp, phdr->p_offset, SEEK_SET);
+			fseek(fp, offset, SEEK_SET);
so the concern is that the realloc buf_size will be smaller than the 'buf' offset of phdr->p_offset value, right? Anyway:

at first I got unsure because of what realloc man page says, i.e. the common part will have the same contents, i.e. before and after what is in a a given offset will remain the same if in an area <= new size.

But yeah, if phdr->p_filesz < offsetof(Elf32_Phdr, p_offset) (unlikely, I guess), then accessing phdr->p_offset after the realloc may be unsafe (perhaps when using some off-limits memory access tool that paints freed memory?).

Anyway, the new code is clear and more robust, applying.

Quoted 1 line

Acked-by Jiri Olsa <[email protected]>

Thanks,

Quoted 1 line

jirka

tip-bot for Mitchell Krome

merge bot

2014-12-18 06:33 UTC #3 lore raw

[tip:perf/urgent] perf symbols: Fix use after free in filename__read_build_id

In reply to Mitchell Krome

perf symbols: Fix use after free in filename__read_build_id

Commit-ID:  7ad74b41e56e4f7f42c6b765bc44428cd09310d7
Gitweb:     http://git.kernel.org/tip/7ad74b41e56e4f7f42c6b765bc44428cd09310d7
Author:     Mitchell Krome <[email protected]>
AuthorDate: Tue, 16 Dec 2014 12:16:12 +1000
Committer:  Arnaldo Carvalho de Melo <[email protected]>
CommitDate: Wed, 17 Dec 2014 11:58:17 -0300

perf symbols: Fix use after free in filename__read_build_id

Signed-off-by Mitchell Krome <[email protected]>

Cc Jiri Olsa <[email protected]>

Cc Ingo Molnar <[email protected]>

Cc Jiri Olsa <[email protected]>

Cc Paul Mackerras <[email protected]>

Cc Peter Zijlstra <[email protected]>

Link http://lkml.kernel.org/r/20141216021612.GA7199@mitchell open here

Signed-off-by Arnaldo Carvalho de Melo <[email protected]>

---
 tools/perf/util/symbol-minimal.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

tools/perf/util/symbol-minimal.c +6 -2

index fa585c6..d7efb03 100644
@@ -129,6 +129,7 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
 
 		for (i = 0, phdr = buf; i < ehdr.e_phnum; i++, phdr++) {
 			void *tmp;
+			long offset;
 
 			if (need_swap) {
 				phdr->p_type = bswap_32(phdr->p_type);

@@ -140,12 +141,13 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
 				continue;
 
 			buf_size = phdr->p_filesz;
+			offset = phdr->p_offset;
 			tmp = realloc(buf, buf_size);
 			if (tmp == NULL)
 				goto out_free;
 
 			buf = tmp;
-			fseek(fp, phdr->p_offset, SEEK_SET);
+			fseek(fp, offset, SEEK_SET);
 			if (fread(buf, buf_size, 1, fp) != 1)
 				goto out_free;

@@ -178,6 +180,7 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
 
 		for (i = 0, phdr = buf; i < ehdr.e_phnum; i++, phdr++) {
 			void *tmp;
+			long offset;
 
 			if (need_swap) {
 				phdr->p_type = bswap_32(phdr->p_type);

@@ -189,12 +192,13 @@ int filename__read_build_id(const char *filename, void *bf, size_t size)
 				continue;
 
 			buf_size = phdr->p_filesz;
+			offset = phdr->p_offset;
 			tmp = realloc(buf, buf_size);
 			if (tmp == NULL)
 				goto out_free;
 
 			buf = tmp;
-			fseek(fp, phdr->p_offset, SEEK_SET);
+			fseek(fp, offset, SEEK_SET);
 			if (fread(buf, buf_size, 1, fp) != 1)
 				goto out_free;