exif_process_IFD_TAG() currently accepts a dir_entry, offset_base
and IFDlength. However, it's very hard to follow how these values
are related to each other and the addressable memory region. As we
add additional bounds check, this gets further confused.
One of the basic cases is where dir_entry is in
[offset_base, offset_base+IFDlength), in which case the memory
[dir_entry, offset_base+IFDlength) is valid, but the memory
[offset_base, dir_entry) is not necessarily valid. I wasn't able
to understand what exactly is valid if dir_entry is outside
[offset_base, offset_base+IFDlength)
This patch changes everything to use a struct that separately stores
offset_base and the valid memory region and adds helpers to fetch
offsets and check that pointers are in-bounds.
Closes GH-5068.
* PHP-7.4:
Fix test
Fix bug #78793
Fix build - no model field anymore
Fixed bug #78910Fix#78878: Buffer underflow in bc_shift_addsub
Fix test
Fix#78862: link() silently truncates after a null byte on Windows
Fix#78863: DirectoryIterator class silently truncates after a null byte
Fix#78943: mail() may release string with refcount==1 twice
* PHP-7.3:
Fixed bug #78910Fix#78878: Buffer underflow in bc_shift_addsub
Fix test
Fix#78862: link() silently truncates after a null byte on Windows
Fix#78863: DirectoryIterator class silently truncates after a null byte
Fix#78943: mail() may release string with refcount==1 twice
* PHP-7.2:
Fixed bug #78910Fix#78878: Buffer underflow in bc_shift_addsub
Fix test
Fix#78862: link() silently truncates after a null byte on Windows
Fix#78863: DirectoryIterator class silently truncates after a null byte
Emitting errors is fairly expensive, to the point that parsing
a file with a huge number of invalid tags can take seconds.
Generating ten thousand errors is unlikely to help anybody, but
constitutes a potential DOS vector.
This fixes two leaks related to duplicate tags, as well as a leak
of zero-length FMT_(S)BYTE with non-null value. This can show up
for MAKERNOTE values where the original length is non-zero, but
the first character is a null byte.
