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Fix GH-19570: unable to fseek in /dev/zero and /dev/null #19736

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14 changes: 14 additions & 0 deletions ext/standard/tests/streams/gh19570.phpt
View file Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,14 @@
--TEST--
GH-19570 (unable to fseek in /dev/zero and /dev/null)
--SKIPIF--
<?php
if (PHP_OS_FAMILY !== "Linux") die("skip only for Linux");
?>
--FILE--
<?php
var_dump(fseek(fopen("/dev/zero", "rb"), 1*1024*1024, SEEK_SET));
var_dump(fseek(fopen("/dev/null", "rb"), 1*1024*1024, SEEK_SET));
?>
--EXPECT--
int(0)
int(0)
15 changes: 15 additions & 0 deletions main/streams/plain_wrapper.c
View file Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -43,6 +43,10 @@
# include <limits.h>
#endif

#ifdef __linux__
# include <sys/sysmacros.h>
#endif

#define php_stream_fopen_from_fd_int(fd, mode, persistent_id) _php_stream_fopen_from_fd_int((fd), (mode), (persistent_id) STREAMS_CC)
#define php_stream_fopen_from_fd_int_rel(fd, mode, persistent_id) _php_stream_fopen_from_fd_int((fd), (mode), (persistent_id) STREAMS_REL_CC)
#define php_stream_fopen_from_file_int(file, mode) _php_stream_fopen_from_file_int((file), (mode) STREAMS_CC)
Expand Down Expand Up @@ -255,7 +259,18 @@ PHPAPI php_stream *_php_stream_fopen_tmpfile(int dummy STREAMS_DC)
static void detect_is_seekable(php_stdio_stream_data *self) {
#if defined(S_ISFIFO) && defined(S_ISCHR)
if (self->fd >= 0 && do_fstat(self, 0) == 0) {
#ifdef __linux__
if (S_ISCHR(self->sb.st_mode)) {
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@devnexen devnexen Sep 6, 2025

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note that not just linux, allows some character devices being seekable, e.g. freebsd and very likely macos. The equivalent for freebsd at least, can t rely on device versions at all but on a "poorer" solution such as if fseek returns -1 and errno is ESPIPE then it is not seekable.

/* /dev/null & /dev/zero are exceptions, check their major/minor ID
* https://www.kernel.org/doc/Documentation/admin-guide/devices.txt */
self->is_seekable = major(self->sb.st_rdev) == 1
&& (minor(self->sb.st_rdev) == 3 || minor(self->sb.st_rdev) == 5);
} else {
self->is_seekable = !S_ISFIFO(self->sb.st_mode);
}
#else
self->is_seekable = !(S_ISFIFO(self->sb.st_mode) || S_ISCHR(self->sb.st_mode));
#endif
self->is_pipe = S_ISFIFO(self->sb.st_mode);
}
#elif defined(PHP_WIN32)
Expand Down
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