[PATCH 18/23] tools lib api: Fix mount_overload() snprintf truncation and toupper range

[Arnaldo Carvalho de Melo]

From: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>

mount_overload() builds an environment variable name like
"PERF_SYSFS_ENVIRONMENT" from fs->name.  Two bugs:

1) snprintf() uses name_len as the buffer size instead of sizeof(upper_name).
   For fs->name = "sysfs" (len=5), the output is truncated to "PERF" (4
   chars + null), so getenv() never finds the intended variable.

2) mem_toupper() only uppercases name_len bytes, converting just the "PERF"
   prefix rather than the full string including the filesystem name portion.

Fix by using sizeof(upper_name) for snprintf and strlen(upper_name) for
mem_toupper, so the full "PERF_SYSFS_ENVIRONMENT" string is correctly
formatted and uppercased.

Reported-by: sashiko-bot <sashiko-bot@xxxxxxxxxx>
Fixes: 73ca85ad364769ff ("tools lib api fs: Add FSTYPE__mount() method")
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Assisted-by: Claude Opus 4.6 <noreply@xxxxxxxxxxxxx>
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/lib/api/fs/fs.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/lib/api/fs/fs.c b/tools/lib/api/fs/fs.c
index d16911818d4d3569..cbd8eab0d1df0c6b 100644
--- a/tools/lib/api/fs/fs.c
+++ b/tools/lib/api/fs/fs.c
@@ -261,8 +261,8 @@ static const char *mount_overload(struct fs *fs)
 	/* "PERF_" + name + "_ENVIRONMENT" + '\0' */
 	char upper_name[5 + name_len + 12 + 1];
 
-	snprintf(upper_name, name_len, "PERF_%s_ENVIRONMENT", fs->name);
-	mem_toupper(upper_name, name_len);
+	snprintf(upper_name, sizeof(upper_name), "PERF_%s_ENVIRONMENT", fs->name);
+	mem_toupper(upper_name, strlen(upper_name));
 
 	return getenv(upper_name) ?: *fs->mounts;
 }
-- 
2.54.0