Re: bug in [ -f file ] test

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Re: bug in [ -f file ] test

From:	László Házy
Subject:	Re: bug in [ -f file ] test
Date:	Thu, 28 Jul 2016 12:52:42 -0400

Thanks for the effort Chet. Here are the results of some tests I have done, including what you requested. Note that I have SELinux as disabled.

[root]$ getenforce
Disabled

[user1]# cat /home/user1/file

This is file.

[user2]# cat /home/user1/file

This is file.

[user1]# cat /var/tmp/link

cat: /var/tmp/link: Permission denied

[user2]$ cat /var/tmp/link

This is file.

[user1]$ stat /home/user1/file

File: ‘/home/user1/file’

Size: 14 Blocks: 8 IO Block: 4096 regular file

Device: 803h/2051d Inode: 3414083 Links: 1

Access: (0644/-rw-r--r--) Uid: ( 501/ user1) Gid: ( 100/ users)

Access: 2016-07-28 12:08:34.186872745 -0400

Modify: 2016-07-28 12:08:30.879845375 -0400

Change: 2016-07-28 12:08:30.950845962 -0400

Birth: -

[user2]# stat /home/user1/file

File: ‘/home/user1/file’

Size: 14 Blocks: 8 IO Block: 4096 regular file

Device: 803h/2051d Inode: 3414083 Links: 1

Access: (0644/-rw-r--r--) Uid: ( 501/ user1) Gid: ( 100/ users)

Access: 2016-07-28 12:08:34.186872745 -0400

Modify: 2016-07-28 12:08:30.879845375 -0400

Change: 2016-07-28 12:08:30.950845962 -0400

Birth: -

[user1]# stat /var/tmp/link

File: ‘/var/tmp/link’ -> ‘/home/user1/file’

Size: 17 Blocks: 0 IO Block: 4096 symbolic link

Device: 808h/2056d Inode: 131183 Links: 1

Access: (0777/lrwxrwxrwx) Uid: ( 500/ user2) Gid: ( 100/ users)

Access: 2016-07-27 12:17:07.899994243 -0400

Modify: 2016-07-27 12:17:07.398991028 -0400

Change: 2016-07-27 12:17:07.398991028 -0400

Birth: -

[user2]# stat /var/tmp/link

File: ‘/var/tmp/link’ -> ‘/home/user1/file’

Size: 17 Blocks: 0 IO Block: 4096 symbolic link

Device: 808h/2056d Inode: 131183 Links: 1

Access: (0777/lrwxrwxrwx) Uid: ( 500/ user2) Gid: ( 100/ users)

Access: 2016-07-27 12:17:07.899994243 -0400

Modify: 2016-07-27 12:17:07.398991028 -0400

Change: 2016-07-27 12:17:07.398991028 -0400

Birth: -

Then, I created the /home/user1/test.sh script with the following content:

#!/bin/bash

[[ -f /var/tmp/link ]]

echo $?

End of /home/user1/test.sh.

[user1]$ strace ./test.sh

execve("./test.sh", ["./test.sh"], [/* 59 vars */]) = 0

brk(NULL) = 0x80d51000

mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb77b5000

access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)

open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3

fstat64(3, {st_mode=S_IFREG|0644, st_size=128315, ...}) = 0

mmap2(NULL, 128315, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7795000

close(3) = 0

open("/lib/libtinfo.so.5", O_RDONLY|O_CLOEXEC) = 3

read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\220^\0\0004\0\0\0"..., 512) = 512

fstat64(3, {st_mode=S_IFREG|0755, st_size=142888, ...}) = 0

mmap2(NULL, 141008, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb7772000

mmap2(0xb7791000, 16384, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1f000) = 0xb7791000

close(3) = 0

open("/lib/libdl.so.2", O_RDONLY|O_CLOEXEC) = 3

read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\220\n\0\0004\0\0\0"..., 512) = 512

fstat64(3, {st_mode=S_IFREG|0755, st_size=18272, ...}) = 0

mmap2(NULL, 16508, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb776d000

mmap2(0xb7770000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2000) = 0xb7770000

close(3) = 0

open("/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3

read(3, "\177ELF\1\1\1\3\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\260\206\1\0004\0\0\0"..., 512) = 512

fstat64(3, {st_mode=S_IFREG|0755, st_size=2125576, ...}) = 0

mmap2(NULL, 1886780, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb75a0000

mmap2(0xb7767000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1c7000) = 0xb7767000

mmap2(0xb776a000, 10812, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb776a000

close(3) = 0

mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb759f000

mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb759e000

set_thread_area({entry_number:-1, base_addr:0xb759e700, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0 (entry_number:6)

mprotect(0xb7767000, 8192, PROT_READ) = 0

mprotect(0xb7770000, 4096, PROT_READ) = 0

mprotect(0xb7791000, 12288, PROT_READ) = 0

mprotect(0x801be000, 8192, PROT_READ) = 0

mprotect(0xb77dc000, 4096, PROT_READ) = 0

munmap(0xb7795000, 128315) = 0

open("/dev/tty", O_RDWR|O_NONBLOCK|O_LARGEFILE) = 3

close(3) = 0

brk(NULL) = 0x80d51000

brk(0x80d72000) = 0x80d72000

brk(NULL) = 0x80d72000

open("/usr/lib/locale/locale-archive", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = 3

fstat64(3, {st_mode=S_IFREG|0644, st_size=111950656, ...}) = 0

mmap2(NULL, 2097152, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb739e000

mmap2(NULL, 1253376, PROT_READ, MAP_PRIVATE, 3, 0x1079000) = 0xb726c000

close(3) = 0

getuid32() = 501

getgid32() = 100

geteuid32() = 501

getegid32() = 100

rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0

brk(NULL) = 0x80d72000

open("/proc/meminfo", O_RDONLY|O_CLOEXEC) = 3

fstat64(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0

mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb77b4000

read(3, "MemTotal: 8239856 kB\nMemF"..., 1024) = 1024

close(3) = 0

munmap(0xb77b4000, 4096) = 0

rt_sigaction(SIGCHLD, {SIG_DFL, [], SA_RESTART}, {SIG_DFL, [], 0}, 8) = 0

rt_sigaction(SIGCHLD, {SIG_DFL, [], SA_RESTART}, {SIG_DFL, [], SA_RESTART}, 8) = 0

rt_sigaction(SIGINT, {SIG_DFL, [], 0}, {SIG_DFL, [], 0}, 8) = 0

rt_sigaction(SIGQUIT, {SIG_DFL, [], 0}, {SIG_DFL, [], 0}, 8) = 0

rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0

rt_sigaction(SIGQUIT, {SIG_IGN, [], 0}, {SIG_DFL, [], 0}, 8) = 0

uname({sysname="Linux", nodename="ws021", ...}) = 0

rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0

open("/usr/lib/gconv/gconv-modules.cache", O_RDONLY) = 3

fstat64(3, {st_mode=S_IFREG|0644, st_size=26252, ...}) = 0

mmap2(NULL, 26252, PROT_READ, MAP_SHARED, 3, 0) = 0xb77ae000

close(3) = 0

rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0

stat64("/home/user1", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0

stat64(".", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0

getpid() = 8430

getppid() = 8428

getpgrp() = 8428

rt_sigaction(SIGCHLD, {0x80107930, [], SA_RESTART}, {SIG_DFL, [], SA_RESTART}, 8) = 0

ugetrlimit(RLIMIT_NPROC, {rlim_cur=64221, rlim_max=64221}) = 0

rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0

open("./test.sh", O_RDONLY|O_LARGEFILE) = 3

ioctl(3, TCGETS, 0xbfaeb1ec) = -1 ENOTTY (Inappropriate ioctl for device)

_llseek(3, 0, [0], SEEK_CUR) = 0

read(3, "#!/bin/bash\n\n[[ -f /var/tmp/link"..., 80) = 45

_llseek(3, 0, [0], SEEK_SET) = 0

ugetrlimit(RLIMIT_NOFILE, {rlim_cur=1024, rlim_max=4*1024}) = 0

fcntl64(255, F_GETFD) = -1 EBADF (Bad file descriptor)

dup2(3, 255) = 255

close(3) = 0

fcntl64(255, F_SETFD, FD_CLOEXEC) = 0

fcntl64(255, F_GETFL) = 0x8000 (flags O_RDONLY|O_LARGEFILE)

fstat64(255, {st_mode=S_IFREG|0755, st_size=45, ...}) = 0

_llseek(255, 0, [0], SEEK_CUR) = 0

read(255, "#!/bin/bash\n\n[[ -f /var/tmp/link"..., 45) = 45

stat64("/var/tmp/link", 0xbfaeb038) = -1 EACCES (Permission denied)

fstat64(1, {st_mode=S_IFCHR|0600, st_rdev=makedev(136, 0), ...}) = 0

mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb77ad000

write(1, "1\n", 21

) = 2

read(255, "", 45) = 0

rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0

rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0

exit_group(0) = ?

+++ exited with 0 +++

[user2]# cd /home/user1

[user2]# strace ./test.sh

execve("./test.sh", ["./test.sh"], [/* 58 vars */]) = 0

brk(NULL) = 0x80d1c000

mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7778000

access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)

open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3

fstat64(3, {st_mode=S_IFREG|0644, st_size=128315, ...}) = 0

mmap2(NULL, 128315, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7758000

close(3) = 0

open("/lib/libtinfo.so.5", O_RDONLY|O_CLOEXEC) = 3

read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\220^\0\0004\0\0\0"..., 512) = 512

fstat64(3, {st_mode=S_IFREG|0755, st_size=142888, ...}) = 0

mmap2(NULL, 141008, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb7735000

mmap2(0xb7754000, 16384, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1f000) = 0xb7754000

close(3) = 0

open("/lib/libdl.so.2", O_RDONLY|O_CLOEXEC) = 3

read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\220\n\0\0004\0\0\0"..., 512) = 512

fstat64(3, {st_mode=S_IFREG|0755, st_size=18272, ...}) = 0

mmap2(NULL, 16508, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb7730000

mmap2(0xb7733000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2000) = 0xb7733000

close(3) = 0

open("/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3

read(3, "\177ELF\1\1\1\3\0\0\0\0\0\0\0\0\3\0\3\0\1\0\0\0\260\206\1\0004\0\0\0"..., 512) = 512

fstat64(3, {st_mode=S_IFREG|0755, st_size=2125576, ...}) = 0

mmap2(NULL, 1886780, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0xb7563000

mmap2(0xb772a000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1c7000) = 0xb772a000

mmap2(0xb772d000, 10812, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xb772d000

close(3) = 0

mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7562000

mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7561000

set_thread_area({entry_number:-1, base_addr:0xb7561700, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}) = 0 (entry_number:6)

mprotect(0xb772a000, 8192, PROT_READ) = 0

mprotect(0xb7733000, 4096, PROT_READ) = 0

mprotect(0xb7754000, 12288, PROT_READ) = 0

mprotect(0x801ba000, 8192, PROT_READ) = 0

mprotect(0xb779f000, 4096, PROT_READ) = 0

munmap(0xb7758000, 128315) = 0

open("/dev/tty", O_RDWR|O_NONBLOCK|O_LARGEFILE) = 3

close(3) = 0

brk(NULL) = 0x80d1c000

brk(0x80d3d000) = 0x80d3d000

brk(NULL) = 0x80d3d000

open("/usr/lib/locale/locale-archive", O_RDONLY|O_LARGEFILE|O_CLOEXEC) = 3

fstat64(3, {st_mode=S_IFREG|0644, st_size=111950656, ...}) = 0

mmap2(NULL, 2097152, PROT_READ, MAP_PRIVATE, 3, 0) = 0xb7361000

mmap2(NULL, 1253376, PROT_READ, MAP_PRIVATE, 3, 0x1079000) = 0xb722f000

close(3) = 0

getuid32() = 500

getgid32() = 100

geteuid32() = 500

getegid32() = 100

rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0

brk(NULL) = 0x80d3d000

open("/proc/meminfo", O_RDONLY|O_CLOEXEC) = 3

fstat64(3, {st_mode=S_IFREG|0444, st_size=0, ...}) = 0

mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7777000

read(3, "MemTotal: 8239856 kB\nMemF"..., 1024) = 1024

close(3) = 0

munmap(0xb7777000, 4096) = 0

rt_sigaction(SIGCHLD, {SIG_DFL, [], SA_RESTART}, {SIG_DFL, [], 0}, 8) = 0

rt_sigaction(SIGCHLD, {SIG_DFL, [], SA_RESTART}, {SIG_DFL, [], SA_RESTART}, 8) = 0

rt_sigaction(SIGINT, {SIG_DFL, [], 0}, {SIG_DFL, [], 0}, 8) = 0

rt_sigaction(SIGQUIT, {SIG_DFL, [], 0}, {SIG_DFL, [], 0}, 8) = 0

rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0

rt_sigaction(SIGQUIT, {SIG_IGN, [], 0}, {SIG_DFL, [], 0}, 8) = 0

uname({sysname="Linux", nodename="ws021", ...}) = 0

rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0

open("/usr/lib/gconv/gconv-modules.cache", O_RDONLY) = 3

fstat64(3, {st_mode=S_IFREG|0644, st_size=26252, ...}) = 0

mmap2(NULL, 26252, PROT_READ, MAP_SHARED, 3, 0) = 0xb7771000

close(3) = 0

rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0

stat64("/home/user1", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0

stat64(".", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0

getpid() = 8451

getppid() = 8449

getpgrp() = 8449

rt_sigaction(SIGCHLD, {0x80103930, [], SA_RESTART}, {SIG_DFL, [], SA_RESTART}, 8) = 0

ugetrlimit(RLIMIT_NPROC, {rlim_cur=64221, rlim_max=64221}) = 0

rt_sigprocmask(SIG_BLOCK, NULL, [], 8) = 0

open("./test.sh", O_RDONLY|O_LARGEFILE) = 3

ioctl(3, TCGETS, 0xbff880dc) = -1 ENOTTY (Inappropriate ioctl for device)

_llseek(3, 0, [0], SEEK_CUR) = 0

read(3, "#!/bin/bash\n\n[[ -f /var/tmp/link"..., 80) = 45

_llseek(3, 0, [0], SEEK_SET) = 0

ugetrlimit(RLIMIT_NOFILE, {rlim_cur=1024, rlim_max=4*1024}) = 0

fcntl64(255, F_GETFD) = -1 EBADF (Bad file descriptor)

dup2(3, 255) = 255

close(3) = 0

fcntl64(255, F_SETFD, FD_CLOEXEC) = 0

fcntl64(255, F_GETFL) = 0x8000 (flags O_RDONLY|O_LARGEFILE)

fstat64(255, {st_mode=S_IFREG|0755, st_size=45, ...}) = 0

_llseek(255, 0, [0], SEEK_CUR) = 0

read(255, "#!/bin/bash\n\n[[ -f /var/tmp/link"..., 45) = 45

stat64("/var/tmp/link", {st_mode=S_IFREG|0644, st_size=14, ...}) = 0

fstat64(1, {st_mode=S_IFCHR|0600, st_rdev=makedev(136, 3), ...}) = 0

mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7770000

write(1, "0\n", 20

) = 2

read(255, "", 45) = 0

rt_sigprocmask(SIG_BLOCK, [CHLD], [], 8) = 0

rt_sigprocmask(SIG_SETMASK, [], NULL, 8) = 0

exit_group(0) = ?

+++ exited with 0 +++

On Wed, 2016-07-27 at 18:33 -0400, Chet Ramey wrote:

On 7/27/16 3:34 PM, László Házy wrote:

You have probably not done the first command: "[user1]$ chmod g+rx
/home/user1". In my case, there is no access problem. I can ls and cd.
Thing is, even root gets the wrong answer if it does the "is file?" query.


I performed that command, but I tore it all down and rebuilt it anyway.
Running a system call tracer (strace) shows that stat ("/var/tmp/link", )
returns -1 with errno == EACCES.  `cat' displays "Permission Denied", and
`cp' says "cannot stat".

What does strace show when you run it as user1 with a script that contains

[[ -f /var/tmp/link ]]
echo $?

?

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