diff options
| -rw-r--r-- | lib/libc/stdio/mktemp.3 | 65 |
1 files changed, 64 insertions, 1 deletions
diff --git a/lib/libc/stdio/mktemp.3 b/lib/libc/stdio/mktemp.3 index 3bed7904fdc..e7d612d7ccc 100644 --- a/lib/libc/stdio/mktemp.3 +++ b/lib/libc/stdio/mktemp.3 @@ -1,4 +1,4 @@ -.\" $OpenBSD: mktemp.3,v 1.11 1998/06/30 23:03:11 deraadt Exp $ +.\" $OpenBSD: mktemp.3,v 1.12 1998/12/15 19:19:50 deraadt Exp $ .\" .\" Copyright (c) 1989, 1991, 1993 .\" The Regents of the University of California. All rights reserved. @@ -206,6 +206,69 @@ and .Fn mkstemps functions are nonstandard and should not be used if portability is required. +.Sh EXAMPLES +Quite often a programmer will want to replace a use of +.Fn mktemp +with +.Fn mkstemp , +usually to avoid the problems described above. +Doing this correctly requires a good understanding of the +code in question. +.Pp +For instance code of this form +.Bd -literal -offset indent +char sfn[15] = ""; +FILE *sfp; + +strcpy(sfn, "/tmp/ed.XXXXXX"); +if (mktemp(sfn) == NULL || (sfp = fopen(sfn, "w+")) == NULL) { + fprintf(stderr, "%s: %s\n", sfn, strerror(errno)); + return (NULL); +} +return (sfp); +.Ed +.Pp +should be rewritten like this: +.Bd -literal -offset indent +char sfn[15] = ""; +FILE *sfp; +int fd = -1; + +strcpy(sfn, "/tmp/ed.XXXXXX"); +if ((fd = mkstemp(sfn)) == -1 || + (sfp = fdopen(fd, "w+")) == NULL) { + if (fd != -1) { + unlink(sfn); + close(fd); + } + fprintf(stderr, "%s: %s\n", sfn, strerror(errno)); + return (NULL); +} +return (sfp); +.Ed +.Pp +Often one will find code which uses +.Fn mktemp +very early on, perhaps to globally initialize the template nicely, but the +code which calls +.Xr open 2 +or +.Xr fopen 3 +on that filename will occur much later. Modifying such code for +.Fn mkstemp +can be difficult. +(In almost all cases, the use of of +.Xr fopen 3 +will mean that the flags +.Dv O_CREAT | O_EXCL +are not open, and thus a symbolic link race becomes possible; hence making +neccessary the use of +.Xr fdopen 3 +as seen above). +Furthermore, one must be careful about code which opens, closes, and then +re-opens the file in question. +Finally, one must ensure that upon error the temporary file is +removed correctly. .Sh SEE ALSO .Xr chmod 2 , .Xr getpid 2 , |