Bug 2059542

+++ This bug was initially created as a clone of Bug #2058686 +++

Sample reproducer, as normal user run:

$ df --direct /root

Program received signal SIGSEGV, Segmentation fault.
0x00000000004092ea in quotearg_buffer_restyled (buffer=buffer@entry=0x618720 <slot0> "‘/root’", buffersize=buffersize@entry=256, arg=arg@entry=0x0, argsize=argsize@entry=18446744073709551615, quoting_style=locale_quoting_style, 
    flags=flags@entry=1, quote_these_too=quote_these_too@entry=0x6185a8 <quote_quoting_options+8>, left_quote=0x413a1e "‘", right_quote=0x413a13 "’") at lib/quotearg.c:343
343	  for (i = 0;  ! (argsize == SIZE_MAX ? arg[i] == '\0' : i == argsize);  i++)
(gdb) bt
#0  0x00000000004092ea in quotearg_buffer_restyled (buffer=buffer@entry=0x618720 <slot0> "‘/root’", buffersize=buffersize@entry=256, arg=arg@entry=0x0, argsize=argsize@entry=18446744073709551615, quoting_style=locale_quoting_style, 
    flags=flags@entry=1, quote_these_too=quote_these_too@entry=0x6185a8 <quote_quoting_options+8>, left_quote=0x413a1e "‘", right_quote=0x413a13 "’") at lib/quotearg.c:343
#1  0x0000000000409d0d in quotearg_n_options (n=n@entry=0, arg=arg@entry=0x0, argsize=argsize@entry=18446744073709551615, options=options@entry=0x6185a0 <quote_quoting_options>) at lib/quotearg.c:802
#2  0x000000000040a3fc in quote_n_mem (n=n@entry=0, arg=arg@entry=0x0, argsize=argsize@entry=18446744073709551615) at lib/quotearg.c:949
#3  0x000000000040a41c in quote_n (n=n@entry=0, arg=arg@entry=0x0) at lib/quotearg.c:961
#4  0x000000000040a42a in quote (arg=arg@entry=0x0) at lib/quotearg.c:967
#5  0x0000000000404845 in get_dev (disk=disk@entry=0x0, mount_point=mount_point@entry=0x0, file=file@entry=0x61de60 "/root", stat_file=stat_file@entry=0x0, fstype=fstype@entry=0x0, me_dummy=me_dummy@entry=false, 
    me_remote=me_remote@entry=false, force_fsu=force_fsu@entry=0x0, process_all=process_all@entry=false) at src/df.c:951
#6  0x0000000000403064 in get_entry (statp=0x61c380, name=0x7fffffffe4a5 "/root") at src/df.c:1370
#7  main (argc=3, argv=<optimized out>) at src/df.c:1747

  The problem is incorrect handling of the condition of not being able
to resolve the mount point of the file/path argument.

  This should be a minor issue, and has several way to fix it. Probably
the proper way is to use another approach in the find_mount_point
function, to not need to chdir to path components, and/or use something
like realpath to then get the stat of the directory of the --direct
argument.

  A simple fix would be to just not segfault and handle the NULL return
from find_mount_point as well as the other NULL values, due to --direct
usage.

--- Additional comment from Kamil Dudka on 2022-02-25 17:25:40 CET ---

Sounds like a bug in our downstream patch.  Thank you for reporting it!

--- Additional comment from Kamil Dudka on 2022-03-01 10:08:38 CET ---

The same command works on RHEL-6.  The bug seems to be introduced in this Fedora commit:

    https://src.fedoraproject.org/rpms/coreutils/c/bb33bc40ad58cce4bc59c119c4180fdea43e23a1

--- Additional comment from Kamil Dudka on 2022-03-01 10:35:16 CET ---

The behavior of `df --direct` has been incorrect since RHEL-7 also when the file argument was accessible.

el6 $ strace -e statfs df --direct /usr
statfs("/usr", {f_type="EXT2_SUPER_MAGIC", f_bsize=4096, f_blocks=4484716, f_bfree=2051743, f_bavail=1822265, f_files=1148304, f_ffree=908509, f_fsid={-169108419, 43772881}, f_namelen=255, f_frsize=4096}) = 0
Filesystem     1K-blocks    Used Available Use% File
-               17938864 9731892   7289060  58% /usr
+++ exited with 0 +++

el7 $ strace -e statfs df --direct /usr
statfs("/", {f_type=BTRFS_SUPER_MAGIC, f_bsize=4096, f_blocks=21330562, f_bfree=12613318, f_bavail=11678096, f_files=0, f_ffree=0, f_fsid={val=[2661982033, 1034311026]}, f_namelen=255, f_frsize=4096, f_flags=ST_VALID|ST_RELATIME}) = 0
Filesystem     1K-blocks     Used Available Use% File
-               85322248 34868976  46712384  43% /
+++ exited with 0 +++

el8 $ strace -e statfs df --direct /usr
statfs("/", {f_type=XFS_SB_MAGIC, f_bsize=4096, f_blocks=39055233, f_bfree=35459353, f_bavail=35459353, f_files=78118400, f_ffree=77818477, f_fsid={val=[0xfd02, 0]}, f_namelen=255, f_frsize=4096, f_flags=ST_VALID|ST_RELATIME}) = 0
Filesystem     1K-blocks     Used Available Use% File
-              156220932 14383520 141837412  10% /
+++ exited with 0 +++

--- Additional comment from Kamil Dudka on 2022-03-01 10:51:53 CET ---

Fedora commits:
https://src.fedoraproject.org/rpms/coreutils/c/c25beef1ca94b1a34b2fe5ffa91dfe39965e1f6a?branch=rawhide
https://src.fedoraproject.org/rpms/coreutils/c/c25beef1ca94b1a34b2fe5ffa91dfe39965e1f6a?branch=f36
https://src.fedoraproject.org/rpms/coreutils/c/85fa418a5a02242147e10f8561ffe9ff5357263c?branch=f35
https://src.fedoraproject.org/rpms/coreutils/c/964f7a01a59ce9038d7c7467f8f790b1d7c30ff7?branch=f34