Messages in this thread | | | Date | Fri, 07 Mar 2008 00:35:56 +0100 | From | Roel Kluin <> | Subject | Re: [PATCH] locomo.c: convert strncpy(x, y, sizeof(x)) to strlcpy |
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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));
Roel
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