In kallsyms__parse(), the loop reading symbol names iterates with
i < sizeof(symbol_name), which allows i to reach sizeof(symbol_name)
upon loop exit. The subsequent symbol_name[i] = '\0' then writes one
byte past the end of the stack-allocated symbol_name[] array.

Fix this by changing the loop bound to KSYM_NAME_LEN, so
the null terminator always lands within the array. The overflow is
triggerable by a kallsyms entry with a symbol name of KSYM_NAME_LEN+1
or more characters (e.g., long Rust mangled names or a malicious
/proc/kallsyms).

Fixes: 53df2b934412 ("libsymbols kallsyms: Parse using io api")
Signed-off-by: Rui Qi <qirui.001@bytedance.com>

---

Changes in v4:
- Use KSYM_NAME_LEN for the loop bound as well, as suggested by Namhyung.

Changes in v3:
- Use KSYM_NAME_LEN instead of sizeof(symbol_name) - 1 for the
  overflow check, as suggested by Namhyung.

Changes in v2:
- Added read_to_eol(&io) when a symbol name exceeds the buffer size,
  preventing remaining characters from being parsed as the next symbol entry.
- Added Fixes tag.
---
 tools/lib/symbol/kallsyms.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/lib/symbol/kallsyms.c b/tools/lib/symbol/kallsyms.c
index e335ac2b9e19..d64bd9cc82a9 100644
--- a/tools/lib/symbol/kallsyms.c
+++ b/tools/lib/symbol/kallsyms.c
@@ -60,7 +60,7 @@ int kallsyms__parse(const char *filename, void *arg,
 			read_to_eol(&io);
 			continue;
 		}
-		for (i = 0; i < sizeof(symbol_name); i++) {
+		for (i = 0; i < KSYM_NAME_LEN; i++) {
 			ch = io__get_char(&io);
 			if (ch < 0 || ch == '\n')
 				break;
@@ -68,6 +68,9 @@ int kallsyms__parse(const char *filename, void *arg,
 		}
 		symbol_name[i]  = '\0';
 
+		if (i == KSYM_NAME_LEN)
+			read_to_eol(&io);
+
 		err = process_symbol(arg, symbol_name, symbol_type, start);
 		if (err)
 			break;
-- 
2.20.1

On Thu, May 28, 2026 at 02:23:55PM +0800, Rui Qi wrote:
> In kallsyms__parse(), the loop reading symbol names iterates with
> i < sizeof(symbol_name), which allows i to reach sizeof(symbol_name)
> upon loop exit. The subsequent symbol_name[i] = '\0' then writes one
> byte past the end of the stack-allocated symbol_name[] array.
> 
> Fix this by changing the loop bound to KSYM_NAME_LEN, so
> the null terminator always lands within the array. The overflow is
> triggerable by a kallsyms entry with a symbol name of KSYM_NAME_LEN+1
> or more characters (e.g., long Rust mangled names or a malicious
> /proc/kallsyms).
> 
> Fixes: 53df2b934412 ("libsymbols kallsyms: Parse using io api")
> Signed-off-by: Rui Qi <qirui.001@bytedance.com>

Acked-by: Namhyung Kim <namhyung@kernel.org>

Thanks,
Namhyung

> 
> ---
> 
> Changes in v4:
> - Use KSYM_NAME_LEN for the loop bound as well, as suggested by Namhyung.
> 
> Changes in v3:
> - Use KSYM_NAME_LEN instead of sizeof(symbol_name) - 1 for the
>   overflow check, as suggested by Namhyung.
> 
> Changes in v2:
> - Added read_to_eol(&io) when a symbol name exceeds the buffer size,
>   preventing remaining characters from being parsed as the next symbol entry.
> - Added Fixes tag.
> ---
>  tools/lib/symbol/kallsyms.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/lib/symbol/kallsyms.c b/tools/lib/symbol/kallsyms.c
> index e335ac2b9e19..d64bd9cc82a9 100644
> --- a/tools/lib/symbol/kallsyms.c
> +++ b/tools/lib/symbol/kallsyms.c
> @@ -60,7 +60,7 @@ int kallsyms__parse(const char *filename, void *arg,
>  			read_to_eol(&io);
>  			continue;
>  		}
> -		for (i = 0; i < sizeof(symbol_name); i++) {
> +		for (i = 0; i < KSYM_NAME_LEN; i++) {
>  			ch = io__get_char(&io);
>  			if (ch < 0 || ch == '\n')
>  				break;
> @@ -68,6 +68,9 @@ int kallsyms__parse(const char *filename, void *arg,
>  		}
>  		symbol_name[i]  = '\0';
>  
> +		if (i == KSYM_NAME_LEN)
> +			read_to_eol(&io);
> +
>  		err = process_symbol(arg, symbol_name, symbol_type, start);
>  		if (err)
>  			break;
> -- 
> 2.20.1

On Thu, May 28, 2026 at 10:34:55AM -0700, Namhyung Kim wrote:
> On Thu, May 28, 2026 at 02:23:55PM +0800, Rui Qi wrote:
> > In kallsyms__parse(), the loop reading symbol names iterates with
> > i < sizeof(symbol_name), which allows i to reach sizeof(symbol_name)
> > upon loop exit. The subsequent symbol_name[i] = '\0' then writes one
> > byte past the end of the stack-allocated symbol_name[] array.
> > 
> > Fix this by changing the loop bound to KSYM_NAME_LEN, so
> > the null terminator always lands within the array. The overflow is
> > triggerable by a kallsyms entry with a symbol name of KSYM_NAME_LEN+1
> > or more characters (e.g., long Rust mangled names or a malicious
> > /proc/kallsyms).
> > 
> > Fixes: 53df2b934412 ("libsymbols kallsyms: Parse using io api")
> > Signed-off-by: Rui Qi <qirui.001@bytedance.com>
> 
> Acked-by: Namhyung Kim <namhyung@kernel.org>

Thanks, applied to perf-tools-next, for v7.2.

- Arnaldo