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From: "jasonwhite at fb dot com" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug dynamic-link/26322] New: Libraries may fail to load if (p)read
 doesn't return all bytes requested
Date: Thu, 30 Jul 2020 18:04:21 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D26322

            Bug ID: 26322
           Summary: Libraries may fail to load if (p)read doesn't return
                    all bytes requested
           Product: glibc
           Version: 2.33
            Status: UNCONFIRMED
          Severity: minor
          Priority: P2
         Component: dynamic-link
          Assignee: unassigned at sourceware dot org
          Reporter: jasonwhite at fb dot com
  Target Milestone: ---

In `elf/dl-load.c` there is a call to pread[1]:

    if ((size_t) __pread64_nocancel (fd, (void *) phdr, maplength,
                                    ehdr->e_phoff) !=3D maplength)
      {
      read_error:
          errval =3D errno;
          errstring =3D N_("cannot read file data");
          goto call_lose;
      }

However, there is no guarantee that pread will return all the bytes request=
ed.
Thus, I believe the read should be wrapped in a loop to ensure it receives =
all
the bytes requested.

I found this issue while simulating a pathological kernel that only returns=
 one
byte at a time for read calls using ptrace. I imagine this could also be
reproduced by writing a small FUSE file system that only returns a byte at a
time for reads.

[1]:
https://sourceware.org/git/?p=3Dglibc.git;a=3Dblob;f=3Delf/dl-load.c;h=3Dc1=
bc8c26be1229fafc2a03afd9fb27edbcf8c3a8;hb=3D95c1056962a3f2297c94ce47f0eaf0c=
5b6563231#l1667

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