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From: Roel Kluin <>
To: "H. Peter Anvin" <>
	Linux-arm <>,
	lkml <>
Subject: Re: [PATCH] locomo.c: convert strncpy(x, y, sizeof(x)) to strlcpy
Date: Fri, 07 Mar 2008 00:35:56 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

H. Peter Anvin wrote:
> Roel Kluin wrote:
>> This patch was not yet tested. Please confirm it's right.
>> ---
>> strncpy does not append '\0' if the length of the source string equals
>> the size parameter, strlcpy does.
> Are you sure it's safe to not zero out the contents of the buffer (no
> information leak)?
>     -hpa

As I understand it, please correct me if I'm wrong:

Of the three variants: strcpy, strncpy and strlcpy.
- strcpy does not append \0 (unless the source string already contained it)
- strncpy appends \0's if the source string is smaller than the size
  parameter (for all remaining characters)
- strlcpy always appends a single \0 (unless size parameter was 0)

char *strcpy(char *dest, const char *src);
char *strncpy(char *dest, const char *src, size_t n);
size_t strlcpy(char *dst, const char *src, size_t n);

In the original code strncpy was used and the size parameter was equal
to the source string size:

strncpy(dev->dev.bus_id, info->name, sizeof(dev->dev.bus_id));

Since this the size was equal there was no \0 termination. To \0
terminate using strncpy we could write:

strncpy(dev->dev.bus_id, info->name, sizeof(dev->dev.bus_id) - 1);
dev->dev.bus_id[sizeof(dev->dev.bus_id) - 1] = '\0';

or using strlcpy, which does the same thing:

strlcpy(dev->dev.bus_id, info->name, sizeof(dev->dev.bus_id));


  reply	other threads:[~2008-03-06 23:36 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-03-06 13:08 Roel Kluin
2008-03-06 21:44 ` H. Peter Anvin
2008-03-06 23:35   ` Roel Kluin [this message]
2008-03-07  1:51     ` David Wagner

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