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From: Alexey Dobriyan <adobriyan@gmail.com>
To: akpm@linux-foundation.org
Cc: linux-kernel@vger.kernel.org
Subject: [PATCH 4/5] proc: simpler iterations for /proc/*/cmdline
Date: Wed, 21 Feb 2018 22:30:09 +0300
Message-ID: <20180221193009.GA28678@avx2> (raw)
In-Reply-To: <20180221192751.GC28548@avx2>

"rv" variable is used both as a counter of bytes transferred and
an error value holder but it can be reduced solely to error values
if original start of userspace buffer is stashed and used at the very
end.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

 fs/proc/base.c |   36 +++++++++++++++++-------------------
 1 file changed, 17 insertions(+), 19 deletions(-)

--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -241,8 +241,9 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
 	unsigned long arg_start, arg_end, env_start, env_end;
 	unsigned long len1, len2, len;
 	unsigned long p;
+	char __user *buf0 = buf;
 	char c;
-	ssize_t rv;
+	int rv;
 
 	BUG_ON(*pos < 0);
 
@@ -272,25 +273,20 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
 	len2 = env_end - env_start;
 
 	/* Empty ARGV. */
-	if (len1 == 0) {
-		rv = 0;
-		goto out_free_page;
-	}
+	if (len1 == 0)
+		goto end;
+
 	/*
 	 * Inherently racy -- command line shares address space
 	 * with code and data.
 	 */
-	if (access_remote_vm(mm, arg_end - 1, &c, 1, 0) != 1) {
-		rv = 0;
-		goto out_free_page;
-	}
-
-	rv = 0;
+	if (access_remote_vm(mm, arg_end - 1, &c, 1, 0) != 1)
+		goto end;
 
 	if (c == '\0') {
 		/* Command line (set of strings) occupies whole ARGV. */
 		if (len1 <= *pos)
-			goto out_free_page;
+			goto end;
 
 		p = arg_start + *pos;
 		len = len1 - *pos;
@@ -300,7 +296,7 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
 			nr_read = min3(count, len, PAGE_SIZE);
 			nr_read = access_remote_vm(mm, p, page, nr_read, 0);
 			if (nr_read == 0)
-				goto out_free_page;
+				goto end;
 
 			if (copy_to_user(buf, page, nr_read)) {
 				rv = -EFAULT;
@@ -311,7 +307,6 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
 			len	-= nr_read;
 			buf	+= nr_read;
 			count	-= nr_read;
-			rv	+= nr_read;
 		}
 	} else {
 		/*
@@ -342,7 +337,7 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
 				nr_read = min3(count, len, PAGE_SIZE);
 				nr_read = access_remote_vm(mm, p, page, nr_read, 0);
 				if (nr_read == 0)
-					goto out_free_page;
+					goto end;
 
 				/*
 				 * Command line can be shorter than whole ARGV
@@ -359,10 +354,9 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
 				len	-= nr_write;
 				buf	+= nr_write;
 				count	-= nr_write;
-				rv	+= nr_write;
 
 				if (nr_write < nr_read)
-					goto out_free_page;
+					goto end;
 			}
 
 			/* Only first chunk can be read partially. */
@@ -371,12 +365,16 @@ static ssize_t proc_pid_cmdline_read(struct file *file, char __user *buf,
 		}
 	}
 
+end:
+	free_page((unsigned long)page);
+	mmput(mm);
+	*pos += buf - buf0;
+	return buf - buf0;
+
 out_free_page:
 	free_page((unsigned long)page);
 out_mmput:
 	mmput(mm);
-	if (rv > 0)
-		*pos += rv;
 	return rv;
 }
 

  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-02-21 19:23 [PATCH 1/5] proc: make /proc/*/cmdline go through LSM Alexey Dobriyan
2018-02-21 19:26 ` [PATCH 2/5] proc: more "unsigned int" in /proc/*/cmdline Alexey Dobriyan
2018-02-21 19:27   ` [PATCH 3/5] proc: somewhat simpler code for /proc/*/cmdline Alexey Dobriyan
2018-02-21 19:30     ` Alexey Dobriyan [this message]
2018-02-21 19:33       ` [PATCH 5/5] proc: deduplicate /proc/*/cmdline implementation Alexey Dobriyan
2018-04-20  0:15       ` [PATCH 4/5] proc: simpler iterations for /proc/*/cmdline Andrew Morton
2018-04-20 19:46         ` Alexey Dobriyan
2018-02-21 19:28 ` [PATCH 1/5] proc: make /proc/*/cmdline go through LSM Andy Shevchenko
2018-02-21 19:39   ` Alexey Dobriyan
2018-02-21 20:06 ` Andrew Morton
2018-02-23 19:43   ` [PATCH v2 " Alexey Dobriyan
2018-04-20  0:02 ` [PATCH " Andrew Morton
2018-04-20 19:25   ` Alexey Dobriyan

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