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Subject[PATCH] Documentation/checkpatch: Prefer str_has_prefix over strncmp
Date
Add strncmp() to Documentation/process/deprecated.rst since
using strncmp() to check whether a string starts with a
prefix is error-prone.
The safe replacement is str_has_prefix().

Also add check to the newly introduced deprecated_string_apis
in checkpatch.pl.

This patch depends on patch:
"Documentation/checkpatch: Prefer stracpy/strscpy over
strcpy/strlcpy/strncpy."

Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
---
Documentation/process/deprecated.rst | 8 ++++++++
scripts/checkpatch.pl | 1 +
2 files changed, 9 insertions(+)

diff --git a/Documentation/process/deprecated.rst b/Documentation/process/deprecated.rst
index 56280e108d5a..22d3f0dbcf61 100644
--- a/Documentation/process/deprecated.rst
+++ b/Documentation/process/deprecated.rst
@@ -109,6 +109,14 @@ the given limit of bytes to copy. This is inefficient and can lead to
linear read overflows if a source string is not NUL-terminated. The
safe replacement is stracpy() or strscpy().

+strncmp()
+---------
+:c:func:`strncmp` is often used to test if a string starts with a prefix
+by strncmp(str, prefix, length of prefix). This is error-prone because
+length of prefix can have counting error if using a constant length, or use
+sizeof(prefix) without - 1. Also, if the prefix is a pointer, sizeof(prefix)
+leads to a wrong size. The safe replacement is str_has_prefix().
+
Variable Length Arrays (VLAs)
-----------------------------
Using stack VLAs produces much worse machine code than statically
diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 0ae9ae01d855..38e82d2ac286 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -609,6 +609,7 @@ our %deprecated_string_apis = (
"strcpy" => "stracpy or strscpy",
"strlcpy" => "stracpy or strscpy",
"strncpy" => "stracpy or strscpy - for non-NUL-terminated uses, strncpy dest should be __nonstring",
+ "strncmp" => "str_has_prefix",
);

#Create a search pattern for all these strings apis to speed up a loop below
--
2.20.1
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