linux-kernel - [PATCH] pstore/ram: Avoid needless alloc during header write

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Date:   Tue, 12 Feb 2019 13:48:08 -0800
From:   Kees Cook <keescook@...omium.org>
To:     linux-kernel@...r.kernel.org
Cc:     Yue Hu <huyue2@...ong.com>, Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>
Subject: [PATCH] pstore/ram: Avoid needless alloc during header write

Since the header is a fixed small maximum size, just use a stack variable
to avoid memory allocation in the write path.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 fs/pstore/ram.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index ec0e1da0596a..c5c685589e36 100644
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -345,19 +345,15 @@ static ssize_t ramoops_pstore_read(struct pstore_record *record)
 static size_t ramoops_write_kmsg_hdr(struct persistent_ram_zone *prz,
 				     struct pstore_record *record)
 {
-	char *hdr;
+	char hdr[36]; /* "===="(4), %lld(20), "."(1), %06lu(6), "-%c\n"(3) */
 	size_t len;
 
-	hdr = kasprintf(GFP_ATOMIC, RAMOOPS_KERNMSG_HDR "%lld.%06lu-%c\n",
+	len = scnprintf(hdr, sizeof(hdr),
+		RAMOOPS_KERNMSG_HDR "%lld.%06lu-%c\n",
 		(time64_t)record->time.tv_sec,
 		record->time.tv_nsec / 1000,
 		record->compressed ? 'C' : 'D');
-	if (WARN_ON_ONCE(!hdr))
-		return 0;
-
-	len = strlen(hdr);
 	persistent_ram_write(prz, hdr, len);
-	kfree(hdr);
 
 	return len;
 }
-- 
2.17.1


-- 
Kees Cook