Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>You need the three-argument form of <a href="http://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html" rel="noreferrer"><code>open()</code></a> when you specify O_CREAT. When you omit the third argument, <code>open()</code> uses whatever value happens to be on the stack where the third argument was expected; this is seldom a coherent set of permissions (in your example, it appears that decimal 12 = octal 014 was on the stack).</p> <p>The third argument is the permissions on the file - which will be modified by the <code>umask()</code> value.</p> <pre><code>int fd2 = open("/tmp/test.svg", O_RDWR | O_CREAT, S_IRUSR | S_IRGRP | S_IROTH); </code></pre> <p>Note that you can create a file without write permissions (to anyone else, or any other process) while still being able to write to it from the current process. There is seldom a need to use execute bits on files created from a program - unless you are writing a compiler (and '.svg' files are not normally executables!).</p> <p>The S_xxxx flags come from <a href="http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/sys_stat.h.html#tag_13_62" rel="noreferrer"><code>&lt;sys/stat.h&gt;</code></a> and <a href="http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/fcntl.h.html#tag_13_11" rel="noreferrer"><code>&lt;fcntl.h&gt;</code></a> — you can use either header to get the information (but <code>open()</code> itself is declared in <code>&lt;fcntl.h&gt;</code>).</p> <p>Note that the fixed file name and the absence of protective options such as <code>O_EXCL</code> make even the revised <code>open()</code> call somewhat unsafe.</p>
    singulars
    1. This table or related slice is empty.
    1. POCreate a file in Linux using C
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USJonathan Leffler
    1. USJonathan Leffler
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POCreate a file in Linux using C
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COIf you have recent versions of both the glibc headers and gcc, gcc can warn you about leaving out that third argument to `open`.
      singulars
      1. PO
      1. UScaf
    2. CO@Jonathan: is there something wrong in what i have posted? You have mentioned about following malicious broken symlinks and problem with fixed name in production code. What/why are these problems?
      singulars
      1. PO
      1. USN 1.1
    3. CO@nvl: Let's say that two users, bill and joe, both run your program at the same time. Both create a file /tmp/test.svg...whose data is used? Let's say Mr Malicious works on your machine, and manages to do: `ln -s /etc/passwd /tmp/test.svg`. Now one of two things is going to happen when your program runs: (1) you get an open error because you can't write to /etc/passwd (you aren't root), or (2) you get a copy of your SVG image in /etc/passwd because you are root. Neither is normally considered desirable. And Mr Malicious can also do: `ln -s /usr/lib/security/libmalpam.so /tmp/test.svg`...
      singulars
      1. PO
      1. USJonathan Leffler
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload