[patch -next 1/2] ath9k/debug: improve the snprintf() handling

[patch -next 1/2] ath9k/debug: improve the snprintf() handling

[Dan Carpenter]

The snprintf() function returns the number of bytes that *would* have
been written (not counting the NULL terminator) and that can potentally
be more than the size of the buffer.

In this patch if there were one liners where string clearly fits into
the buffer, then I changed snprintf to sprintf().  It's confusing to use
the return value of snprintf() as a limitter without verifying that it's 
smaller than size.  This is what initially caught my attention here.
If we use the return value of sprintf() instead future code auditors will
assume we've verified that it fits already.

Also I did find some places where it made sense to use the return value 
after we've verified that it is smaller than the buffer size.

Finally the read_file_rcstat() function added an explicit NULL terminator
before calling snprintf().  That's unnecessary because snprintf() will 
add the null terminator automatically.

Signed-off-by: Dan Carpenter <error27@gmail.com>

diff --git a/drivers/net/wireless/ath/ath9k/debug.c b/drivers/net/wireless/ath/ath9k/debug.c
index 2ca9bba..f344128 100644
--- a/drivers/net/wireless/ath/ath9k/debug.c
+++ b/drivers/net/wireless/ath/ath9k/debug.c
@@ -41,7 +41,7 @@ static ssize_t read_file_debug(struct file *file, char __user *user_buf,
 	char buf[32];
 	unsigned int len;
 
-	len = snprintf(buf, sizeof(buf), "0x%08x\n", common->debug_mask);
+	len = sprintf(buf, "0x%08x\n", common->debug_mask);
 	return simple_read_from_buffer(user_buf, count, ppos, buf, len);
 }
 
@@ -85,7 +85,7 @@ static ssize_t read_file_tx_chainmask(struct file *file, char __user *user_buf,
 	char buf[32];
 	unsigned int len;
 
-	len = snprintf(buf, sizeof(buf), "0x%08x\n", common->tx_chainmask);
+	len = sprintf(buf, "0x%08x\n", common->tx_chainmask);
 	return simple_read_from_buffer(user_buf, count, ppos, buf, len);
 }
 
@@ -127,7 +127,7 @@ static ssize_t read_file_rx_chainmask(struct file *file, char __user *user_buf,
 	char buf[32];
 	unsigned int len;
 
-	len = snprintf(buf, sizeof(buf), "0x%08x\n", common->rx_chainmask);
+	len = sprintf(buf, "0x%08x\n", common->rx_chainmask);
 	return simple_read_from_buffer(user_buf, count, ppos, buf, len);
 }
 
@@ -247,6 +247,9 @@ static ssize_t read_file_dma(struct file *file, char __user *user_buf,
 
 	ath9k_ps_restore(sc);
 
+	if (len > DMA_BUF_LEN)
+		len = DMA_BUF_LEN;
+
 	retval = simple_read_from_buffer(user_buf, count, ppos, buf, len);
 	kfree(buf);
 	return retval;
@@ -357,6 +360,9 @@ static ssize_t read_file_interrupt(struct file *file, char __user *user_buf,
 	len += snprintf(buf + len, sizeof(buf) - len,
 		"%8s: %10u\n", "TOTAL", sc->debug.stats.istats.total);
 
+	if (len > sizeof(buf))
+		len = sizeof(buf);
+
 	return simple_read_from_buffer(user_buf, count, ppos, buf, len);
 }
 
@@ -396,11 +402,10 @@ static ssize_t read_file_rcstat(struct file *file, char __user *user_buf,
 	if (sc->cur_rate_table == NULL)
 		return 0;
 
-	max = 80 + sc->cur_rate_table->rate_cnt * 1024;
-	buf = kmalloc(max + 1, GFP_KERNEL);
+	max = 80 + sc->cur_rate_table->rate_cnt * 1024 + 1;
+	buf = kmalloc(max, GFP_KERNEL);
 	if (buf == NULL)
 		return 0;
-	buf[max] = 0;
 
 	len += sprintf(buf, "%6s %6s %6s "
 		       "%10s %10s %10s %10s\n",
@@ -442,6 +447,9 @@ static ssize_t read_file_rcstat(struct file *file, char __user *user_buf,
 			stats->per);
 	}
 
+	if (len > max)
+		len = max;
+
 	retval = simple_read_from_buffer(user_buf, count, ppos, buf, len);
 	kfree(buf);
 	return retval;
@@ -504,6 +512,9 @@ static ssize_t read_file_wiphy(struct file *file, char __user *user_buf,
 	len += snprintf(buf + len, sizeof(buf) - len,
 			"addrmask: %pM\n", addr);
 
+	if (len > sizeof(buf))
+		len = sizeof(buf);
+
 	return simple_read_from_buffer(user_buf, count, ppos, buf, len);
 }
 
@@ -647,6 +658,9 @@ static ssize_t read_file_xmit(struct file *file, char __user *user_buf,
 	PR("DATA Underrun:   ", data_underrun);
 	PR("DELIM Underrun:  ", delim_underrun);
 
+	if (len > size)
+		len = size;
+
 	retval = simple_read_from_buffer(user_buf, count, ppos, buf, len);
 	kfree(buf);
 
@@ -750,6 +764,9 @@ static ssize_t read_file_recv(struct file *file, char __user *user_buf,
 	PHY_ERR("HT-LENGTH", ATH9K_PHYERR_HT_LENGTH_ILLEGAL);
 	PHY_ERR("HT-RATE", ATH9K_PHYERR_HT_RATE_ILLEGAL);
 
+	if (len > size)
+		len = size;
+
 	retval = simple_read_from_buffer(user_buf, count, ppos, buf, len);
 	kfree(buf);
 
@@ -801,7 +818,7 @@ static ssize_t read_file_regidx(struct file *file, char __user *user_buf,
 	char buf[32];
 	unsigned int len;
 
-	len = snprintf(buf, sizeof(buf), "0x%08x\n", sc->debug.regidx);
+	len = sprintf(buf, "0x%08x\n", sc->debug.regidx);
 	return simple_read_from_buffer(user_buf, count, ppos, buf, len);
 }
 
@@ -842,7 +859,7 @@ static ssize_t read_file_regval(struct file *file, char __user *user_buf,
 	u32 regval;
 
 	regval = REG_READ_D(ah, sc->debug.regidx);
-	len = snprintf(buf, sizeof(buf), "0x%08x\n", regval);
+	len = sprintf(buf, "0x%08x\n", regval);
 	return simple_read_from_buffer(user_buf, count, ppos, buf, len);
 }
 

[patch -next 1/2 v2] ath9k/debug: improve the snprintf() handling

[Dan Carpenter]

The snprintf() function returns the number of bytes that *would* have
been written (not counting the NULL terminator).  We want to pass NULL
terminated strings to the user so we need to add one to the snprintf 
return value.  And if the return value is larger than the size of the 
buffer we need to set it to the smaller value.

In this patch if there were one liners where string clearly fits into
the buffer, then I changed snprintf to sprintf().  It's confusing to use
the return value of snprintf() as a limitter without verifying that it's 
smaller than size.  This is what initially caught my attention here.
If we use the return value of sprintf() instead, future code auditors will
assume we've verified that it fits already.

Also I did find some places where it made sense to use the return value 
after we've verified that it is smaller than the buffer size.

Finally the read_file_rcstat() function added an explicit NULL terminator
before calling snprintf().  That's unnecessary because snprintf() will 
add the null terminator automatically.

Signed-off-by: Dan Carpenter <error27@gmail.com>
---
V2: Include NULL terminator in the buffer which gets copied to the user.
Btw. I don't actually this hardware so I can't test this code.  Sorry.  :/

diff --git a/drivers/net/wireless/ath/ath9k/debug.c b/drivers/net/wireless/ath/ath9k/debug.c
index 2ca9bba..fad1c85 100644
--- a/drivers/net/wireless/ath/ath9k/debug.c
+++ b/drivers/net/wireless/ath/ath9k/debug.c
@@ -41,8 +41,8 @@ static ssize_t read_file_debug(struct file *file, char __user *user_buf,
 	char buf[32];
 	unsigned int len;
 
-	len = snprintf(buf, sizeof(buf), "0x%08x\n", common->debug_mask);
-	return simple_read_from_buffer(user_buf, count, ppos, buf, len);
+	len = sprintf(buf, "0x%08x\n", common->debug_mask);
+	return simple_read_from_buffer(user_buf, count, ppos, buf, len + 1);
 }
 
 static ssize_t write_file_debug(struct file *file, const char __user *user_buf,
@@ -85,8 +85,8 @@ static ssize_t read_file_tx_chainmask(struct file *file, char __user *user_buf,
 	char buf[32];
 	unsigned int len;
 
-	len = snprintf(buf, sizeof(buf), "0x%08x\n", common->tx_chainmask);
-	return simple_read_from_buffer(user_buf, count, ppos, buf, len);
+	len = sprintf(buf, "0x%08x\n", common->tx_chainmask);
+	return simple_read_from_buffer(user_buf, count, ppos, buf, len + 1);
 }
 
 static ssize_t write_file_tx_chainmask(struct file *file, const char __user *user_buf,
@@ -127,8 +127,8 @@ static ssize_t read_file_rx_chainmask(struct file *file, char __user *user_buf,
 	char buf[32];
 	unsigned int len;
 
-	len = snprintf(buf, sizeof(buf), "0x%08x\n", common->rx_chainmask);
-	return simple_read_from_buffer(user_buf, count, ppos, buf, len);
+	len = sprintf(buf, "0x%08x\n", common->rx_chainmask);
+	return simple_read_from_buffer(user_buf, count, ppos, buf, len + 1);
 }
 
 static ssize_t write_file_rx_chainmask(struct file *file, const char __user *user_buf,
@@ -247,6 +247,10 @@ static ssize_t read_file_dma(struct file *file, char __user *user_buf,
 
 	ath9k_ps_restore(sc);
 
+	len++;
+	if (len > DMA_BUF_LEN)
+		len = DMA_BUF_LEN;
+
 	retval = simple_read_from_buffer(user_buf, count, ppos, buf, len);
 	kfree(buf);
 	return retval;
@@ -357,6 +361,10 @@ static ssize_t read_file_interrupt(struct file *file, char __user *user_buf,
 	len += snprintf(buf + len, sizeof(buf) - len,
 		"%8s: %10u\n", "TOTAL", sc->debug.stats.istats.total);
 
+	len++;
+	if (len > sizeof(buf))
+		len = sizeof(buf);
+
 	return simple_read_from_buffer(user_buf, count, ppos, buf, len);
 }
 
@@ -396,11 +404,10 @@ static ssize_t read_file_rcstat(struct file *file, char __user *user_buf,
 	if (sc->cur_rate_table == NULL)
 		return 0;
 
-	max = 80 + sc->cur_rate_table->rate_cnt * 1024;
-	buf = kmalloc(max + 1, GFP_KERNEL);
+	max = 80 + sc->cur_rate_table->rate_cnt * 1024 + 1;
+	buf = kmalloc(max, GFP_KERNEL);
 	if (buf == NULL)
 		return 0;
-	buf[max] = 0;
 
 	len += sprintf(buf, "%6s %6s %6s "
 		       "%10s %10s %10s %10s\n",
@@ -442,6 +449,10 @@ static ssize_t read_file_rcstat(struct file *file, char __user *user_buf,
 			stats->per);
 	}
 
+	len++;
+	if (len > max)
+		len = max;
+
 	retval = simple_read_from_buffer(user_buf, count, ppos, buf, len);
 	kfree(buf);
 	return retval;
@@ -504,6 +515,10 @@ static ssize_t read_file_wiphy(struct file *file, char __user *user_buf,
 	len += snprintf(buf + len, sizeof(buf) - len,
 			"addrmask: %pM\n", addr);
 
+	len++;
+	if (len > sizeof(buf))
+		len = sizeof(buf);
+
 	return simple_read_from_buffer(user_buf, count, ppos, buf, len);
 }
 
@@ -647,6 +662,10 @@ static ssize_t read_file_xmit(struct file *file, char __user *user_buf,
 	PR("DATA Underrun:   ", data_underrun);
 	PR("DELIM Underrun:  ", delim_underrun);
 
+	len++;
+	if (len > size)
+		len = size;
+
 	retval = simple_read_from_buffer(user_buf, count, ppos, buf, len);
 	kfree(buf);
 
@@ -750,6 +769,10 @@ static ssize_t read_file_recv(struct file *file, char __user *user_buf,
 	PHY_ERR("HT-LENGTH", ATH9K_PHYERR_HT_LENGTH_ILLEGAL);
 	PHY_ERR("HT-RATE", ATH9K_PHYERR_HT_RATE_ILLEGAL);
 
+	len++;
+	if (len > size)
+		len = size;
+
 	retval = simple_read_from_buffer(user_buf, count, ppos, buf, len);
 	kfree(buf);
 
@@ -801,8 +824,8 @@ static ssize_t read_file_regidx(struct file *file, char __user *user_buf,
 	char buf[32];
 	unsigned int len;
 
-	len = snprintf(buf, sizeof(buf), "0x%08x\n", sc->debug.regidx);
-	return simple_read_from_buffer(user_buf, count, ppos, buf, len);
+	len = sprintf(buf, "0x%08x\n", sc->debug.regidx);
+	return simple_read_from_buffer(user_buf, count, ppos, buf, len + 1);
 }
 
 static ssize_t write_file_regidx(struct file *file, const char __user *user_buf,
@@ -842,8 +865,8 @@ static ssize_t read_file_regval(struct file *file, char __user *user_buf,
 	u32 regval;
 
 	regval = REG_READ_D(ah, sc->debug.regidx);
-	len = snprintf(buf, sizeof(buf), "0x%08x\n", regval);
-	return simple_read_from_buffer(user_buf, count, ppos, buf, len);
+	len = sprintf(buf, "0x%08x\n", regval);
+	return simple_read_from_buffer(user_buf, count, ppos, buf, len + 1);
 }
 
 static ssize_t write_file_regval(struct file *file, const char __user *user_buf,

Re: [patch -next 1/2 v2] ath9k/debug: improve the snprintf() handling

[Dan Carpenter]

On Sat, May 15, 2010 at 03:34:41PM +0200, Dan Carpenter wrote:
> The snprintf() function returns the number of bytes that *would* have
> been written (not counting the NULL terminator).  We want to pass NULL
> terminated strings to the user so we need to add one to the snprintf 
> return value.

Actually this is a filesystem so we don't want to pass null terminated
strings do we?  Probably the first version of this patch was the better
one.

(What I love about open source is the discussions.  But normally it's
not just one discussing and sending out patches to his ownself. :P).

regards,
dan carpenter